I had a problem in my game on one lot where one of the stray pets (Jezebel) came into the portal then it would freeze and I would have to use End Task to end it since it wasn't responding. I would get a noticed the game had stopped working. This happened with almost every stray that came onto the property of the morning. The only way I could solve this issue was to move out the family, replace the house with an exact copy and move them back in. Lucky I keep fresh builds of all my builds but it got to be annoying. lol
The next time this happened it was another little dog (the one in the family bin) every day at 9:06. I had to move the family out again, since removing all my mods did not fix the problem. I thought there might be a conflict. It seems they were trying to 'roll in grass' action but it couldn't be completed so I removed all trees, flowers and any custom trees and grass and everything in the lot, and then built a fence in front of house with a locked gate to keep them from coming through that portal. That seems to have worked for now, hopefully I can put back all my custom trees and grass/flowers etc.
I'm not sure what caused the freeze at same time every day other than a routing issue? (flat land in front) but possible it was some cc grass and flowers which were not cloned from Maxis flowers
or shrubs but used their bhavs.
Glad it wasn't mods.
If anyone else knows why TS2UC wants to crash everyday at same time let me know in case that was not actually the issue. I haven't played long enough after building a fence out front to be 100% this will solve it. It seems to be when they enter the portal (5x4 lot).
ETA: Disabling all cc and mods got me past the 9:06 crash, but seems these dogs cause a Sim passing the house to freeze and resetting that townie doesn't work it still freezes at 9:06 if cc is enabled, (he gets stuck in breathing in the air that came in M&G) so when one or the other stray is in the portal (unseen) it crashes. I hope I have solved this but I have a feeling I haven't. Something to do with Fun With Pets EP in TS2UC and I can't remember the bug this was about.