I have a fairly simple setup in one project. There is a custom field (multiple choices) to select the board:
And then in each board I filter by this field so in the Backlog the team only see the issues related to their team and not all the issues.
The filter seems to work fine but I see some issues in the baclog that shouldn't be there. For example in the Coding board this is the filter:
fixVersion in unreleasedVersions() OR fixVersion is EMPTY AND "Board[Select List (multiple choices)]" = Coding
But in the backlog I see this:

This also includes tickets without any board assigned:
