Only way to get them back is to find all the old save files that might have them. I haven't tried putting new prints into the saved area out of fear of maybe permanently losing the saved prints. I hope they're still there given the log file. I think this explains which file holds the blueprint ...

I have the same issue. All my saved blueprints are missing. Rollback does not help. Not sure what other information I can provide nor if it's related to game version. I had them during 16.2 and probably 16.3.

The log file shows my saved blueprints yet they aren't showing up when open the blueprint ...