Settings - Personalization - Colors
Set Accent Color from Auto to Manual (optionally also turn off Show accent colors on title bar and windows borders). This setting used to be called "Automatically pick an accent color from my background"
Fixed for me.
Sadly, mine was already setup this way:
- Accent colour: Manual
- Show accent colour on title bars and windows borders: Off
I do not believe this is a reliable fix. But if the issue has stopped occurring for you, what else have you changed?