Dad has episodes of memory loss. Sometimes he doesn’t know his family, but the doctor hasn’t diagnosed him with anything. What’s next?

Spence, when you say that your Dad doesn't know his family, in what respect? Names don't ring a bell? Photos are strangers? In person are strangers?

As TaylorUK had mentioned, keep a daily log of what Dad is doing, eating, etc. and see if you notice a pattern of these episodes. It could be as something as simple of a food reaction that trigger these memory black outs.

Not drinking enough water can cause all type of medial issues, so make sure Dad drinks as much water as possible. Some older folks don't want a lot of water, that means more trips to the bathroom.

Is there a pattern of the time of day when the episodes happen? If all seem to happen, let's say after 4pm, that could be what is called "sundowners". My Dad use to get into his time machine and go back to the 1940's after 4pm. So I had to play along with that.

When your Dad doesn't have these episodes, I assume he is doing ok. Correct?

Keep trying - I don't know about tests in US but in UK test for cognitive impairment is so biased towards simple answers not reasoning or logic that many elderly persons can pass them with ease, and be totally different when seen over a 24 hour period. I suggest you take to keeping a diary of your father's "lapses" including the situation and go back to Dr in a month with your "evidence" then take it from there.