Just updated form 115.0.5322.119 to 116.0.5366.35
I have the same issue in both versions: Right click on any page to 'inspect' in an external DevTools window. 1st 'inspect' is ok. If I do a second 'inspect' while external DevTools window is open, Opera closes an reopens with blank page.
If DevTools is not in an external window this bug doesn't appear.