When any ROS interface is made bridge port, it's made as layer 2 entity (on ethernet level). And it looses capability of acting as interface (layer 3 entity) ... that capability is then carried by bridge interface. This fact is not made apparent in UI, but things can misbehave if one doesn't respect that.
The thing is that bridge has multiple "personalities" and the way UI is built, those personalities seem to be interleaved (but in practice, when somebody knows what they are, it's easy to distinguish between them). A long time forum member @sindy wrote a tutorial, trying to explain all of them: RouterOS bridge mysteries explained ... beware it's heavy reading but I recommend to read and try to understand never the less.