It happens for me for save project and save as, the dialog doesn't show when chitubox is maximized, alt-tab doesn't work, the only way I found to make it appear is to press control alt delete, then clicking cancel, the dialog is somehow brought back to the front. Windows 10 pro 1903 64 bits
Also tried after upgrading to win 10 1909, same issue.
It started when the software switched to the black theme I think.
The Photon workshop software from anycubic also suffers from the same symptoms also since they switched to a black theme