This could simply be Gainax: The Thread, but I'm going with one near and dear to my heart:
Tenku Senki Shurato
It suffered the usual curse of blowing your budget early enough and then just finishing with what scraps they had left. The first 28 episodes or so are fantastic, well animated and well drawn. The last 10, aside from one scene at the very end, looks so bad that there times calling it a slide show would be generous.
Compared episode 13's animation
to episode 30
What you're seeing that looks like they're just missing some animation between key frames is like that for the rest of the show, frequently. It was never a downright gorgeous show, by any means and had a somewhat typical budget for a late 80s shonen thing, but man, it hurts so much because the show is really damned good.