First noticed when my survival system stopped showing all but two categories when updating from 1.20.1-4.12.1 to 4.12.4.
After a lot of testing I figured out how to reproduce the symptoms. It seems to only track the group names of the first 16 inventories connected, even if there is duplicate names.

Create a lectern and add 3 bookwyrms. Connect 8 inventories named 'a'. Connect 8 inventories named 'b'. Connect an inventory named 'c', 'd', 'e'. Notice only 'a' and 'b' show up

If you reconnect all the inventories but make sure in the first 16 connected 'a', 'b', 'c', 'd', 'e' all appear, only then do they all show up.