i have a similar/same GUI freezing problem
Pi4B 4GB + Sony TV + LibreElec 9.1.501, controlled via CEC (SonyTv Remote Control), Video out 1080p 60Hz, Audio via HDMI + tvheadend 4.2.x service with Tevii S662 DVB-S/S2
but i observe this freeze in different use cases,
1. browsing EPG Guide - mostly not waiting complete GUI refresh when sending next remote actions
2. switching between Tv channels, when switching too fast/often
3. sometimes, switching to a TV channel, i can hear audio but screen remains in kodi blue