A Cycles node group in a file of mine seems to have lost its data block somehow. The group still shows its inputs and outputs properly, but the name of it has changed to Missing Data-Block, and no group name shows in the data block dropdown. This happened after several crashes in the file, so I assume it is some sort of corruption.
The node group itself is missing from the file completely. I can append it from an earlier version, but then I have the problem of setting all the now broken node groups back to it. This group is used many times, inside many groups, and across many materials.
Is there a proper fix to this? Or, is there a way to replace these broken groups with the appended fixed group?