I only have one hello doorbell, and it pretty much stays connected the whole time.
few more thing you can try,
1st, for the 2.4Ghz to be N only,
2nd you can also try to fix the channel that 2.4Ghz is set to. depends on how crowding the wifi space is in your area, the fixed channel might help.
3rd you can also try to lower the quality of the stream for testing
4th. it might be worth to try to just remove the mesh node if the doorbell can be reached via 2.4Ghz and see if those are affect by the mesh setup
that's all i can think of, hope it helps
