Ok, I think I've narrowed down the weird behaviour. Just touching the lan cable between the SH2 and router makes the internet connection speed erratic. Tried 4 different cables, all of which work fine elsewhere.
Careful "jiggling" of the plug in the SH2 results in a firm connection for hours, until it happens again
VMDG485 in modem mode so can only use one of the lan ports. Would this be considered enough of a fault to replace the SH2?
Or would they say "It works in router mode so live with it"?
Pretty sure it's the SH2 and not the router, because I tried a different router with the same results.
I'm convinced it's the lan port because when the speed is erratic and TBB shows low 40s Mbps and when it's working and 200+Mbps, without any apparent changes in the log or power levels. I was convinced it was external until wriggling the cable effected the results.
It's this image that explains my pointI rebooted the SH2 because the upload speed was really poor*, but check the timestamps it came back at 40Mbps, then I wriggled the lan cable and the speed went up to 200Mbps and stayed there. The space of 20mins doesn't really seem external. Not saying it isn't, maybe there's some behind the scenes line monitoring or something going on
*There's some T3 stuff going on, that's more recent than this issue.
Assuming that was not a rhetorical question It's on top of a tall cupboard, next to the router. It does get quite dusty but the compressed air was a last ditch effort before losing my patience and squirting it with contact cleaner.
Not sure VM would be happy about me doing that though. So I haven't. Yet.
I posted to see if others were going to say they had the same issue, guess it's not a common problem then