Hiya, yeah this seems a 'thing'. There is an open bug report about this but with no clear understanding of what might be causing it. I have wondered if it is caused by the 'new' greeting animations that were brought in by Get Together. The ones were the sims will shake hands or kiss each other on the cheek etc, only that somehow they are glitching out and the animations don't play but they still get the relationship gain or decay. (Anyway, I'll link to the bug report later as I'm experiencing issues with posting links for some reason right now.)