Matrix43,
I've never seen anything like this. We can try to play with two things:
1. Export your tabSRMM templates (Settings - tabSRMM_Templates, tabSRMM_RTLTemplates) to ini files and attach them here, I'll try to reproduce the problem
2. Try different fonts, primarily embedded into Windows 10 (like Segoe UI, for example), or try to use Scriver as a message editor - just for fun, will it have such glitches too?