I'm at 19 reputation and any neutral character in my party I speak to immediately leave. I tried reinstalling the happy patch but it doesn't work. Any idea what's going on?
Branwen has a trigger on one of the states in her dialog file: "HappinessLT(Myself,0)". The trigger is present in vanilla BG1+TotSC. This trigger fires at reputation of 19 or 20 for a neutral character, which set "Happiness" to -80. This causes the "You are no more honorable than the Loki spawn I left behind." dialog to fire and Branwen to leave the party.
Faldorn and Safana have dialog states with the same trigger.
So, it's not a mod or a bug, it's just the way the BG1 dialog triggers were written.