Hi, I have Glyphs 3 3.1.2 (3151). I used mekkablue’s script for interpolation. The interpolation worked but I couldn’t save my file. The operation couldn’t be completed. -[NSNull length]: unrecognized selector sent to instance 0x2089789d0 keeps coming up when I click CMD + S. Any solve for this problem?
Then you managed to get some invalid data into the document. Not sure if that is resolvable.
Do you remember what you did just before this happened?
Can you check if there is a (autosave) file next to the .glyphs file?
Can you try exporting to .otf or .ufo, just to try to save as much of the latest changes?
Hey @GeorgSeifert same problem on my end - I used the instance insert script and now the file doesn’t want to save (same bug came up after inserting the instances).
The operation couldn’t be completed. -[NSNull length]: unrecognized selector sent to instance 0x1de6c3d60
I tried to delete the instances and glyphs crashed - unfortunately the work that I did since inserting the instances was lost 
What script with what settings did you use?