In v2.39, if I do a lot of maintenance in a folder such as deleting dozens of images, and I switch to another program, when I Alt-Tab or click back to XnView, it's frozen. I must force close XnView in Task Manager and reopen it to continue working.
A similar, maybe related problem, is when I have a video file selected, with the Preview opened, and I click in another folder in the navigation pane. XnView freezes and I must force close it in Task Manager again.
The problem is so common when I know I'm going to do a lot of maintenance in the same folder I bookmark it so that when I reopen it I can go back to the same folder and continue working on it. After I'm finished with that folder I remove the bookmark and add another for the new folder I'm going to work with, and so on and so forth.