This is happening because you are trying to use the TapBridge in
'UseBridge' mode with a PointToPointNetDevice, which doesn't support
bridging.
Some documentation about the different modes is here:
https://www.nsnam.org/docs/models/html/tap.html#
I recommend reconfiguring your topology a bit (even if you have to
insert an additional node/LAN) so that you can instead bind a Csma
device to this tap bridge. I don't think PointToPoint will work well
because it is not a device type that uses 48-bit MAC addresses.
- Tom