The log doesn't give me anything more than "getting opinion modifiers". How would I go about identifying the problem modifier?
There are two stages that log "Getting opinion modifiers" (was that a bad idea? YES!). Is it the first one or the second one?
The first one (just after "Getting traits") reads the opinion_modifiers files from your CK2 installation; if it's crashing there, it's probably a parser crash, and I'd check out those files in your install and see if there's anything suspicious that jumps out at you.
The second one (just after "Creating family trees") reads the opinion modifiers from every rel_NNNN block in your save. If ANYTHING goes wrong there, you should get an additional error logged (either "bad LHS character ID" or "bad relationship modifier"), or the modifier will just be set to 0 value. I don't see anything there that could cause a crash.
If you can't figure out where the problem is coming from, let me know which "Getting opinion modifiers" is causing problems, and I'll see if I can put some additional logging in a special build for you.