Despite working with various NLEs since 1998 (An accurate statement but perhaps misleading as it implies I am more proficient than I am so don't let any stupidity displayed surprise you.) something just happened that I have never seen nor heard of before:
I just finished an edit and exported it. Upon reviewing the video I saw something that sorta blew my mind. Out of nowhere and with nothing in the original timeline to foreshadow it, a clip momentarily lost resolution; for about 2 seconds. It was in the middle of a continuous clip, i.e. it wasn't at an edit point between clips. This was otherwise clean HD footage 1280x720 that suddenly, briefly looked like 1/4 res offline footage.
What on earth could be causing this? I exported it twice and both times this happens. I trashed prefs once, the next output did not have this shift but subsequent outputs of other vids had the same issue. The first res shift did coincide with an audio keyframe, but audio?