Hotfix #4 caused lots of problems and Larian had to release a fix for the hotfix right after.
You should start from the bottom, re-adding HF 1, test and re-add HF 2, etc.
There are at least two potential problems here.
1. Running around, e.g. Act 2, with e.g. HF 3 installed may not cause crashes but once you hit Act 3 . . .
2. Sometimes certain data is baked into the save so if you try to load a save that is looking for a certain HF and that HF is not there then . . .
