PPPOE server continuously drops the same exact clients

PPPOE server continuously drops the same exact clients; we have the clients connected via Access Point Ubiquiti 5AC Prism Gen2. We have changed everything, the Prism Gen2, the ethernet cable running from the POE adapter to the Prism Gen2, the POE, the LAN cable from the POE adapter to the mikrotik and also buy a new mikrotik and same problem we tried every thing possible even change radio frequency we have run out of option we run debug mode and its not giving no explanation. When we put the clients that are droping off on another prism that is active they dont drop off does anyone have a solution to problem
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