Hi all, been having issues with a gradual onset over the last few months, suddenly worsening in the last week or two. Need some advice if you wouldn't mind.

I have a 2860ac connected to BT Business Infinity 2.
LAN1 on the 2860 then goes to an HP ProCurve 1GbE switch in my office, which usually just has my laptop hanging off it.
LAN2 goes to a Dell PowerConnect 6224 in server room with a few boxes hanging off it. (3x host VMware cluster, 1x physical mgmt server, occasionally 1 other physical test server, Netgear ReadyNAS, BluRay player, FreeSat box)
WiFi has Printer, 3x Android phones, 2 or 3 laptops, and sometimes a tablet connected to it.
In addition to work VMs, I also run a few game servers for friends (Minecraft, ARK Survival Evolved, Conan Exiles, 7 Days to Die)
Most traffic over the WAN is game server; remaining is VOIP, general surfing, Youtube, file transfer, the usual etc.
One of the VMs has a VPN connected to one of our main offices most of the time (SonicWall).

Couple months ago one of the main game users (in US) started getting frequent disconnects and bad lag, so I ran some checks on that game server - couldn't find any issues and no-one else was complaining, so I chalked it up to his connection. Then another user, (in US), on a different game server, started saying the same altho she said her connection was getting increasingly heavily utilised and not great, altho she'd never had any issues before; checked that game server out, couldn't find any issues there either, so sat back and waited. A couple weeks ago, I've had users closer to home, (in NL and UK), start experiencing disconnects & bad lag as well. I've not noticed any issues during my time online - I do play on one of the Minecraft servers quite a bit and that's fine for me, but I'm on LAN so would expect that, altho it's reassuring that I see no issues as it kinda rules out any problems with the 6224 or server environment.

BT ran their usual checks on the line and found no issues, but the 2860 is reporting a shed-load of errors on the Upstream, image below. I've sent this screenshot to BT 2nd line who've agreed there is a problem somewhere, they're saying the most likely culprit is the 2860. I've swapped my old BTBusinessHub5 back in in place of the 2860 tho, and am getting pretty much the same reports from users. Unfortunately the BTHub doesn't report errors/status to anywhere near the same level of detail as the 2860, at least not that I can see. Regardless, pretty sure the ugly metrics in the image below are actually recorded and held at the street DSLAM anyway, so BT should be able to see these anyway?

So, is there any way I can run diags on the 2860 to check the modem chips or what-have-you? Intention being to absolutely rule out a router problem, and have evidence to give BT to get them to investigate further?

Many thanks in advance

Also, while looking at the BTHub5 logs I've noticed the following in the Firewall log, which appear somewhat concerning to me, but I don't know enough about networking/security to know for sure, any advice on this would also be very much appreciated!

Despite there not being anything obviously relevant in the changelog, I decided to upgrade the FW to the latest version (3.8.6) from the one it was on (3.8.5.1). This looks to have done something significant to the line config, most notably changing the Upstream to FAST rather than Interleaved with a depth of 337. ReTX is also now showing as on for both Up & Down, which can only be a good thing I suppose. Also, the router is now reporting an Attenuation figure for the Upstream which it wasn't before.

The FECS value has changed from nearly 100 million, down to 16236. I believe this value is recorded and held by the DSLAM though, so wouldn't have expected anything I do at this end to have changed that, however I'm suspecting this whole issue has been due to a bug in the 3.8.5.1 FW, and that the 100 million FECS value was actually a reporting error on the routers behalf. The downstream LYSMB value has also changed from 4715 to 16, however I don't know enough to say whether this is good or bad, it just seems like a massive change and I suspect might be related to the change from INTERLEAVE to FAST on the Upstream...

My ping according to Ookla has dropped from a consistent 18-25ms down to 9-10ms. Not a massive difference, but certainly welcome; rate is pretty much unchanged, just a Mbps or two faster on the Upstream, but I've only just done the FW update so suspect this might change over the next week or so.

New line details in image below: