If you have a saved configuration and then change the Windows DPI scaling, the font sizes can get confused. At the moment if it happens then you need to go to Preferences / Display / Colors and Fonts and then use File > Reset Page To Defaults.
It should not happen at random, but presumably the times when it happens coincide with something changing system DPI (e.g. plugging in monitors with different DPIs).
Opus will respond to this better (as well as Windows itself responds) in the future, as part of better support for high DPI and DPI changing.
If you're seeing crashes, please link your account and send any crash dumps to leo@gpsoft.com.au and I will investigate them and report back. You may also be able to solve crashing issues yourself, as they are almost always caused by 3rd party shell extensions or similar components: Crash, exit or high CPU usage when viewing certain directories - Crash, exit or high CPU usage when right-clicking certain files.