I have found a condition with ... on MirrorValue which results in an Internal Server Error.
It appears if the board contains an “orphan” mirror column. While normally if you delete a connect boards column, all connected mirror columns are deleted, it seems possible for them to not be deleted due to an error.
The mirror column, via API still returns a settings_str that points to the deleted connect boards column, it also contains board-column mappings. The API user has access to the boards pointed to.
My suspicion is that something isn’t getting cleaned up correctly under the hood as well. It doesn’t affect all items on the board. (Maybe it only affects items that were previously connected and there is some orphan connection, or the reverse, only those that were not previously connected?)
for reference this is an accounts board in monday crm, so there could be special things happening nobody knows about. The board is also reporting 84% connections used, yet no connect boards columns appear to have any connections - but the owner can see items to select on the visible connect boards columns. if the owner didn’t have access to underlying boards they’d still see the connect boards column. It is almost like there is ghost connect boards column.