Plot hole: When the radar man of the USS Cayuga describes a radar reading to likely be "One of the Russian cruisers", the commanding officer of the USS decides not to pursue it saying, "We are after bigger fish today - I want the Vasilyev". In the film, the Vasilyev is depicted as a destroyer, which is a smaller and lighter ship than a cruiser. In this context, the cruiser would be a "bigger fish" than the Vasilyev and the CO should pursue it instead if he was after the larger, more dangerous vessels as he seems to declare.
Attack Of The Mutant (1) - S2-E2
Plot hole: Skipper spots the Masked Mutant's headquarters the first time he goes past. He then goes back the next day, and the headquarters have vanished. He then goes back a third time, and the headquarters aren't there yet again. However Skipper says "How can it be. It was right here yesterday," although it wasn't.