Did you notice something unusual in Task Manager? CPU usage spikes? Unusually high RAM usage? I've has several issues with my PC:
1) sometimes MSI_ActiveX_***_Service.exe began to each 30-40% of CPU for no reason even when no applications is running and that cause micro-stutters even in windows itself while any game turned into slide-show. Happens rarely and I just need to kill that process to resolve the issue
2) killer network service (aka KillerService.exe) - this damn think caused memory leaks to the point where all 32Gb RAM become locked without an hour after the last reboot (especially if you downloaded anything) and can be released only by another reboot. That turned my PC into slideshow often. Googled how to remove this service completely and since then I have no issues with memory leaks
3) Microsoft_Audio_Core**** service - sometimes starts to use up to 25-30% of CPU capacity for no reasons. Usually happens during active Discord usage. Does not cause any stutters directly but may affect max FPS in come cases, just killing the process resolves the problem (sometimes need to restart Discord or game to restore sound)
If you do not hit bottleneck with your PC specs, than it is possible you have issues with one of services or drivers - cannot say with 100% confidence, but worth investigating
BTW if you have a compatible client version backup for BE RC1 I would recommend to try it to compare performance as in 12.11 BSG did come optimization