The bug
If you close a Minecraft version, the launcher might crash (or freeze?) with a pop-up saying the launcher is not responding. Happens sometimes, tested with 18w19a.
Linked issues
Comments 3
You say this affects 1.6.89-j; is this actually the case? I'd think it would only affect the native launcher, and I haven't experienced it with that one.
Re-resolving as duplicate of MCL-9319 since this issue is definitely happening to more than just a few users.