If I upgrade our Jenkins instance from 2.235.5 to the new stable 2.249.1 release, I get warnings about unreadable data for the Folder plugin after it comes back up. Our various folders then have no content; attempting to navigate into them gives an error (I think it was a 404).
Here is the complaint about the Folder plugin data, issued once for each folder:
ConversionException: Could not call hudson.model.ListView.readResolve() : null
---- Debugging information ----
message : Could not call hudson.model.ListView.readResolve() : null
cause-exception : com.thoughtworks.xstream.converters.reflection.ObjectAccessException
cause-message : Could not call hudson.model.ListView.readResolve() : null
class : hudson.model.ListView
required-type : hudson.model.ListView
converter-type : hudson.util.RobustReflectionConverter
path : /com.cloudbees.hudson.plugins.folder.Folder/folderViews/views/hudson.model.ListView
line number : 34
I have tried the upgrade a couple of times, in case it was some kind of transient issue, but it failed in exactly the same way both times.
(Fortunately, downgrading back to 2.235.5 gets everything back to normal.)