On the first image the link is up at 20/40Mhz Ce before 22:00 saturday, after that time is at 20Mhz
On the second image the second link is up at 20/40Mhz before 8:15 sunday and after 14:00, in between them the link is at 20Mhz
There is no interference or noise.
Conclusion: tx-power not stable on 911G-5HPacD at 40Mhz