Ok, so I am a Microsoft .NET developer (stating that upfront so you know I am not puzzled by tech or networking terminology) so can you explain how and where to measure the "sync speed" to the hub. I'd be interested in looking at that metric.
Advanced settings> technical log> information
Thanks for that, As suspected it says 20mb/80mb for data rate. Its a Hub 6A with v1.0 hardware.
So this doesn't show any potential issues. But I will keep an eye on things.
Check it when you get the speed drop. If it still reports 80/20 it points to probable congestion in the backhaul as suggested by @iniltous rather than a line fault.