Connection/ router more erratic than normal

[#1]

Normally I sync in a range that gives me  a profile of 4500/5000 and of late the sync rates have been at their best. However. Yesterday and today the behaviour of the connection/router has been much more erratic then normal with sudden resyncs and low rates, even down to 320. What might be the explanation of the behaviour, and given the usually stability with the router holding in to negative SNR is the erratic behaviour liable to recur, or a one off?
An extract of a RouterStats log with changes hi-lited is attached

[#2]

Well since then the router has held in with sync @ 6144 and SNR going in to minus territory, but through put early in the week and much before that was reasonable has deteriorated shockingly as can be seen. I had thought it could relate to the Bank Holiday but it seems no better today.
I have never seen such deterioration and wonder if there can be anything other than contention that may cause it, Bothing has changed in my set up either.

[#3]

It wouldn't be anything to do with contention.

[#4]

Had a stupid thought and it paid off. Did a quick disconnect/ connect and the through put has gone back to what it should be with a 5000 profile. Better brains than mine can tell me why it worked, no doubt. :