A drop in sync such as you have experienced, or even more, is typical of interleaving being turned on. Why G.INP hasn't been I don't know.
And there is no 10-day initial period. A myth propagated by BT Wholesale.
The indispensable man or woman passes from the scene, and what happens next is more or less the same thing as was happening before.
My broadband basic info/help site - www.robertos.me.uk.
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Connection - AAISP Home::1 80/20. Sync 57970/13958kbps @ 600m. - BQM