These two properties of bridge are incompatible:
frame-types=admit-only-vlan-tagged pvid=50
… and the rest of bridge VLAN 50 config assumes untagged.
Bridge has multiple personalities, pretty well explained in this article/tutorial. Setting quite a few properties on bridge under /interface/bridge is actually about bridge the “the router-facing port of the switch” and this includes above quote properties. No, frame-types, set on bridge, doesn’t mean anything to other bridge ports (it’s not default setting or something like that).
I suggest you to keep using tagged frames over bridge port … in this case pvid seting doesn’t matter at all, but you have to set bridge port as tagged member of VLAN 50 (under /interface/bridge/vlan)