It does not work correctly spectral-history

Hello ! Recently I faced with the problem:
Problem occurs when the frequency of scanning, one of the routers as if does not see interference.
There are 2 router mikrotik rb951ui-2hnd and RB951Ui-2nD (hap).
firmware and configuration identical ( version 6.35)
screenshots normal router

strange indicators are of the second router

what could be the problem?