CreativeCore 1.9.27
LittleTiles v1.5.0-pre105

Basically like #104, just a different line number in the first line of the stack trace

https://paste.dimdev.org/cohiviqaro.mccrash

Not the same issue, but a new one :( I will try to fix it.

Does it happen every time? No idea how this could happen.

Maybe this version fixes the problem? https://www.dropbox.com/s/aadfxk7eziio7yw/LittleTiles_v1.5.0-pre106_mc1.12.2.jar?dl=1

With that version I don't get a crash, even after multiple openings and closings in a row, so I'd say it works now.

The new version has been uploaded, it should be available soon.