Connection issue in bridge mode

H an

Hello,
I have the following configuration at home.

A Microtik router for manage the wan and local network.
A amplify router in bridge mode at the basement and a amplify meshpoint in the first floor. (Good connection over 5ghz).

Only in the first floor, several mobilephones and tablets sometime get no IP address by entry or new connection.
A restart at the mesh point solve the problem.
If I go to the basement, the mobile and tablets (Nexus 5x, iPad air, galaxy S8) connect without problems.

Anyone a idea to solve the problems?

Thanks
Andi