I experienced a number of total freezes after installing NB 12.2 (have been using 12.0 before), but could not get an error message of any sort, since NB was completely unresponsive to keystrokes or mouse. This changed today, I got an error popup, which I attach. NB was again totally unresponsive, but I could make a screenshot of the popup message.
The black shadow around the error dialog actually is tens or hundreds of the same popup windows behind the first one. They keep piling up at CPU speed until the app runs out of memory or is killed. For a while I could close a few of them, but they kept coming up faster than I could click.
The file in question (see screenshot) looks normal to me. It has the correct owner and permissions and its content is this:
The crash happened directly after starting the IDE, while it was reading in the last project I worked on. No user interaction was involved.
Fedora 29 / KDE.