Increased latency and slow downloads

[techy]

I have Sky Ultrafast Plus (500MB FTTP).  On Friday 24th I had an hours outage at around 03:50 - 04:50.  Since then the downloads have been slow and I have noticed increased latency.  From my monitoring I can see this latency clearly

The outage around 18:00 on Saturday are when I called Sky to ask them to investigate.  They had me factory reset the hub.  I tested speed after this and after about 4 speed tests I did get a 500MB download, however I has since dropped again to around 300Mb.  tests run to Fast.com and Google speedtest.  I monitor the actual rate in task manager during the test and the max rate is not much greater than the reported rate on the speed test sites.   I do notice that the downloads seem to ramp up to speed rather than start downloading at the fast speed straight away.  This again ony started after the hours outage on 24th Feb.   Sky told me that it was a hub uprgrade that took place on 24th.  Not sure what they mean by this.

The outage at 23:00 on Saturday 25th is unknown cause.  I had to reboot hub to restore service

Does anyone have any suggestions what this could be.  Sky not been helpful as I could get the 500Mb once.

I'm connected with a cable and have tested with only my laptop connected.