Any complications with healthcare POA when the agent lives in a different country?

Your not being in the immediate vicinity might be a problem if immediate decisions were necessary. Could a secondary POA be assigned to act as your mother's agent during the part of the year you are away?

annasita: Per Legal Beagle "A POA executed abroad can be used in the United States as long as it is recognized as valid and abides by relevant state law. When the POA is executed, it must be signed at a "notarization appointment" in the presence of a notarizing official at a local United States embassy or consulate."
Disclaimer: I do not profess to have authored the above information.
To the OP (Original Poster, annasita): This may or may not assist you in your query. I do understand that the POA may not have been executed abroad. However, please remember that as Medical Power of Attorney, you are now your mother's agent (or otherwise known as attorney in fact) and you are acting on behalf of the principal, who is your mother.
I saw your reply to Geaton777, wherein you state that YOU can add her husband as secondary agent. That is incorrect since it is the principal, your mother, who must do that if desired.

I just learned about the guardian/guardianship services industry for those who need competent care, but I would consult with an Elder Law Attorney for a reference of a trustworthy company.

A family member — an articulate, educated, competent person — needed specialized surgery and a 2 week post op at Johns Hopkins. Not being in Baltimore became a huge barrier. Communication was hard. I got tearful calls with “they won’t tell me what’s going on” “I need help getting to the loo and they don’t show up for half an hour” “I need shampoo and my hair dryer.” I’d make calls and try to schmooze the nurses — then the nurses asked the family member to ask me not to call.

The biggest potential problem I foresee is how well your mom can manage her medical issues and how much clarity you can get from doctors and healthcare providers.

If mom can’t drive, how goes she get to the doctor?
What if mom needs PT and doesn’t do the at home exercises?
What if mom doesn’t understand enough to ask thoughtful questions at a doctors appointment?
What if mom misunderstands the medical problem and treatment?
What if mom calls 9-1-1 every time she panics?
What if she’s admitted to ER and left til hell starts to freeze? (I went to an ER that was overworked and AWFUL. Blood dripping on the hallway floor and the idiot tells me the janitor who is 20 feet away needs to clean the bathroom first. Left the person I brought in the hall with people everywhere during Covid until I got the floor nurse)
Is mom capable of managing her meds and getting refills?
What if there is a post treatment recovery that takes months? How does she manage daily living?

You may be able to manage the legal side and the technical side overseas but who manages the every day logistics?

In the event that you are far away the thing is that most decisions made by you when she cannot make them herself any longer (which is the only instance when you DO have to make them) is done fine with you not there. My brother was at the other end of my state, but I was able to handle decisions with him, then FOR him, and then to move him into hospice during covid all without being there. The doctors will guide you in what decisions might work/might be best, if you feel you would be able to trust them until you get there, or altogether, and this is the ONE and ONLY WAY you can get information on which TO make these decisions, given that her husband is likely not able to do so now. Be certain you understand her wishes. What she would want done, what she doesn't want done regarding CPR, vent, dialysis, tube feedings. Be certain to write these refusals (or allowances) right into the document as an addendum.
The doctors then can speak with you once you mail them you POA. Most hospitals now keep them on record.
Yes, you can do this, and indeed you can do ALL POA and Trustee work from being away, but it is a more difficult for CERTAIN.
And as to complications. There will be those and plenty of those no matter where and how you attempt any of this. Be ready for anxiety and frustration when you are in the snares of the medical system, esp. now.

She can set up a second level of proxy (both health care and financial matters) in the event that the first one cannot be contacted. EMS would not refuse care in any event. Your mother should consider a system like LifeAlert where she can push a button on a necklace or bracelet if she needs care, especially if she has nobody at home who she can depend on to help her in an emergency. They send somebody around to check and to get her to the hospital if needed, and they also will help contact the people on her contact list. Your mother should set up a Living Will (advance medical directives), so that you and the people who will help her in an emergency will know what her wishes are. In my mother's senior residence, they have a paper holder on the wall near the door and keep the medical directives posted prominently, so if EMS enters they know what to do.

If you have healthcare proxy that is the same thing as a medical PO IMO. I had my Moms that was called Advanced Medical Directive and my nephews who says Medical POA. Both written in NJ but by 2 different lawyers in 2 different counties. As long as Mom is competent all she needs to do is add you to the HIPPA paperwork saying that you can be involved with her healthcare. If she wants u to go into the office with her than u should be allowed to go. If there are COVID restrictions I don't see where that has anything to do with a Medical POA. I just went to the Drs with my nephew. Because COVID restriction was low I was allowed in with him but wore a mask. If it was high, I would not have been allowed in.

I don't think the office staff understand that there is different wording when it comes to a medical POA. Proxy in my opinion is the same thing if it lists what Mom wants and doesn't want when it comes to her care. I really don't see what the difference is in you writing a POA and having signatures witness by a notary. Was that not done when the proxy was drawn up?

Are you an entire continent away? Or just over the US border? I think complications can come in the form of travel to appear in person to perform certain functions (like notarizing anything); time-zone differences; language barriers, etc.

"She thinks that in an emergency, she would not receive care if they couldn't reach me and I told her that's not the point of the POA, they can't refuse her care."

It may be less about refusing care than making decisions on her behalf about her care that could be the problem. If your mom is cognitively fine, why is she needing a PoA? Your reasons about covid seem...unusual. In the US she can assign you as her Medical Representative, which is a simple HIPAA form she asks for at the doctor's clinic and fills in your name to be her rep at that doctor's office. No notarization or lawyers required, she just signs the form and turns it in to the clinic. This form would allow her medical staff to communicate her protected private medical info to you without her having to be present. It doesn't allow you to make medical decisions on her behalf.

You should ask an attorney. We ran into DPOA problems with living in one STATE and our LO being in another STATE. And that isn't even another country. Even though it is only part of the year that a different country is involved, an attorney would be the best person to discuss this with.

Look into getting a geriatric care manager that can assist you and mom with advocacy when she need it.

https://www.aginglifecare.org/