So this is weird. I started a game, and soon noticed that all but one of my neighbors weren't expanding their territory... eventually, a couple of them became unstuck and started to act normally again, but out of 9 opponents, there are still 7 that are "frozen" (one of them surrendered to another player when attacked by one of the 2 AIS that is working normally) with only their capitols and 1st colonies, can't build ships or planetary improvements, and can't research new technologies. Now that I have played into the game for some time and have a high level of espionage versus several of these AIs, I can inspect their planets, and I can see that while they have stuff in the build queues, the completion time is listed as "Never". I have save games I can submit, but I don't see any way to attach them to a post here. FWIW, the game is working normally other than this glitch (no crashes or other weird behavior.)
Note: I can recall this happening once or twice before, so although it is a rare occurrence it's not just some one-time random glitch.