It is possible there is some corruption of the folder you were last using in PhotoLab.
Suggestion: Create a new folder, and copy a single RAW file into that folder, right-click on the image and Open With PhotoLab9. If that works then try and switch to the ‘bad’ folder.
If it still crashes or the suggestion does not work then open a ticket with DXO and they will ask you to run a diagnostic tool which may help to identify the problem.
It’s a bit of a pain having to go through a full clean install and deleting hidden folders, but sometimes that’s the only way to clear out whatever weird glitch is causing the freeze. It’ll definitely help the next person who runs into this!