This bug also manifests with me, and a lot. Up to the point GoodTask is almost unusable.
I tried to isolate when it happens precisely but it is not clear. In my case, it is for sure when I'm working with tags on a task (adding and removing them). I thought it was when the task went from "having a tag" to "not having a tag" state, but sometimes it happens, sometimes it doesn't.
It could be happening when I'm performing a series of action to the tag (like changing it twice in a row, or adding one and removing a different one, or moving it from the note field to the title field – I changed this setting a couple of days and some of my tasks still have their tags in their note field), but once again, it is not clear.
List view also works fine, and I also need to restart the app to "solve" it (nothing else works). This is why it makes GoodTask unusable, because you just cannot restart your task manager every couple of seconds or minutes.