I'm just really discouraged from doing anything on the save again if this sort of eventual corruption is inevitable. It was just loading the most recent, proper save game (12.5 MB) in Riften that fixed it.

Most recent quicksave was about 12.4 MB and loading the game from there and then exiting the ruin didn't make any difference. The autosave was 12.4/12.5 MB (the game autosaved multiple times there and I'm not sure why, most recent one as 12.5 and the earliest one was 12.4, but both in about the same place). So I'm wondering what caused it on the later saves? They were just after I'd finished up exploring a Dwemer ruin and nothing seemed wrong or out of the ordinary. On a slightly older, proper save (i.e, not a quick or auto save) the game works just fine and I can fast travel wherever even with Dawn of Whiterun installed. I tried fast traveling to Whiterun stables and Markarth and the bug still happened, so I realized it wasn't something exclusive to Whiterun.

Author said in the readme that it didn't use scripts and was relatively safe to uninstall, so I uninstalled it and the same thing happened again. It first happened when I tried to fast travel to Whiterun, which led me to think that maybe it was the Dawn of Whiterun mod that was bugging out the game or something (I downloaded and installed that without taking precautions and when I finally tested it out I figured out it lagged my game from 60 FPS to about 45-50 while in Whiterun, but I didn't want to risk bugging out my save so I left it installed and just dealt with the performance drop), so I looked up the directions to uninstall it and try again. My save of Skyrim is crashing on fast travel and I'm not sure why.

Skyrim crash after fast travel