Is it service affecting? Is your total upstream SNRM being affected by more than a few dB?
If not then best ignore and forget about it, as you will drive yourself nuts and Openreach won't be able to do anything about it.
It could be an emerging HR fault.. it could be REIN with a SHINE spike. Openreach uses DSM for power masks and upstream power levels, which can have an effect on SNRM. You can also have GAIN adjustments from bit-swap. If one band dips, it is far from unusual to see other bands adjust to compensate.
It looks like you had a dip in U1, which for some reason was already higher than it should have been, suggesting that at some point U0 and U2 had also got out of kilter. There was a further dip at 6:25 on U0 & U2, so your modem adjusted U1 to compensate, but eventually it brought it all back in line.
Looking at your graph- and unless the phone rang at that time - , I'd say you had a SHINe burst at ~6:20 which caused some residual REIN on u0 & U2. By 6:24 it was all done with, but it just left the various bands out of kilter.. by 06:45 they were being brought back in line.
Quite often my upstream per band looks horrendous, certain bands will dip and others will rise, they will even cross-over and the pattern reverse on different bands. More often than not it takes a heck of a lot longer for mine to clear. If MDWS was still up I could show you some real pretty pictures on my Upstream bands, that look a heck of a lot more messy than yours.. but there's nothing I can do about it.
