Hey there,
If we assume that it’s client related then, the most likely cause is addons or corrupt data. In that case we need to do a complete UI reset and rebuild everything from scratch. To do this, uninstall any addon managers (Twitch, Wowmatrix, Tukui Client, etc) then reset your UI. If you don’t uninstall addon managers first, it’ll break the UI reset process and we’ll be back at square one.
Now that this is done everything should be fixed. For now, don’t reinstall your addon managers. Instead, you want to manually install the most up to date versions of your addons. Do this one by one and if one breaks it again, reach out to the addon developer to let them know about the problem so they can fix it. After all this is done you should be safe to reinstall any addon managers you use.
Let me know if it’s still a problem after.