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?

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    $\begingroup$ replacing a missing data-block is fairly easy... knowing which data-block is missing is also easy when we have the corrupted file, blender version, hardware, etc. Please share your file and system information for inspection, or try-and-error setting the correct data-block pointers with python. $\endgroup$ – Secrop Jun 27 '18 at 2:22
  • $\begingroup$ @Secrop Where would I find the right info in the file? I can't conveniently share the file without stripping it down because it contains work for a client. $\endgroup$ – Ascalon Jun 27 '18 at 8:49
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    $\begingroup$ I'll suppose that the missing datablock is the nodetree (if it's not, this won't fix anything): append the nodegroup from the uncorrupted file, and in the python console, execute >>> D.materials['FaillingMaterial'].node_tree.nodes['FailingNodegroup'].node_tree = D.nodegroups['AppendedNodegroup'] $\endgroup$ – Secrop Jun 27 '18 at 11:19

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