For example, the latest case (that I extracted the part of the log file referred here) the main building has 5 root bridges on your top, with 3 branches on the neighborhood (2 with 2 non-root bridges, and one with 1).
I don't know the answer to your question.
I only have 1 mesh link in my environment and I don't see any channel changes for the mesh link it in my logs. (for the past 2 weeks)
I recall setting things up so the meshed AP had a 5Ghz mesh and only accepted clients on 2.4Ghz..
If you're accepting clients on the 5Ghz side (same frequency as the mesh) you could be causing yourself problems.
@Bruno I have said this many times before on this forum, but have you used a spectral analyzer to check what is going on? If I'm reading your logs correctly the channel is getting over-utilized. RW have set a limit of 300 and your bridge is getting over that (327). So there is interference from somewhere. Now it might be your own (from other bridges) or from somewhere else (not your bridges).
Why wouldn't it chenge from 100 to 124 I don't know quite exactly, but I don't think the 7731 changes channels at all.