So after the B818 running like a dream for a few weeks (100+Mbps when the cell is quiet), I've had a few issues recently and not sure what to blame, so bear with me - this will be a long one as theres a bit of background!
The 'working' setup consisted of the B818 hooked up via ethernet to an old Vodafone router acting as a AP (DHCP disabled, static IP, etc). In addition to that we have a secondary network that had our NAS (hosting the wifes business website, had to be on PlusNet connection as it needed a static IP), and home HA system on it, so Philips HUE, Fibaro HC2, Heatmiser thermostats, rPi (Homebridge), all via a BT Smart Hub 2 and Netgear GS108 switch. This was all good except to control the house you needed to jump across to the other network, or control it via the 'net which was not too bad. No issues on it or when we used it as our main connection before getting the B818.
Now, missuses website has been redone and we've moved it to a new hosted service, which has means I no longer needed the NAS and the PN connections static IP. I could move everything back onto a single network again but rather than using the BT connection, using the B818. So I hooked up a new ethernet (pre-made) cable from the Voda router to the GS108 and disconnected the BT SH2. This is when the fun started.
Devices will join the wifi just fine. Get an IP address and DNS, etc. Speedtest will initially run ok. After a few minutes the connection becomes flakey. Wifi is strong but the connection is binary - either 100% full speed, or it will crap out and refuse to load something. Putting a device into Airplane mode or just disconnecting/reconnecting will bring it back temporarily. Loading webpages is hit and miss, sometimes it flies, sometimes it completely fails to load, sometimes you get a warning in Chrome that its taking too long but eventually loads. iPlayer has a right fit, will play something fine then stop and crash the TV (admittedly a bit of an old Samsung now, maybe a 2015). So clearly something is not happy, and I'm guessing its something routing related due to the nature of sometimes 100% speed and sometimes nothing, nothing in between. Internal connections - say phone/laptop to NAS are rock solid - full speed all the time.
So I thought it was maybe the Voda router being a bit rubbish at playing man-in-the-middle (as this is 'up' the daisy chain between the B818 and GS108), and anything just needing the GS108 internal network seems fine.
I wanted an excuse to get a proper AP, so went for a Unifi U6-lite. Disconnected the Voda router and hooked up the U6 yesterday initially to the 'backhaul' ethernet going directly to the B818 (taking the rest of the devices offline from the internet), and all appeared well. Being happy with that, I proceeded to put the 'backhaul' connection into the GS108 and put a new ethernet connection to the U6. All appeared ok again, but not long after started to be flakey again - FFS!
I dont have another switch to test, but thought why not try the BT SH2 just as a switch. So connect the 'backhaul' to the BT SH2 and then the SH2 to U6 this morning. All seems fine and has been for a couple of hours (as I write this). I did try then to connect the SH2 to the GS108 and it all seemed to go flakey again.
Sooooo.... my question is this. Given the setup:
FTTC router<>GS108<>devices - works fine
B818<>(router as) AP or U6 <> devices - works fine
B818<>GS108<>U6 (or router as AP)<>devices - flakiness
So why the flakiness on the WAN services but its rock solid on LAN in the last setup? Something between the GS108 and B818 seems not to be happy. Or another device on the GS108 network is causing it but they all played fine on the old FTTC connection.
In my quest to upgrade the home network, I'm fine with buying a new Unifi switch, I have the 'business case' for more ports and PoE, so could easily match the U6-lite with a Switch-lite 16 port. Equally if there's some issue that requires a Unifi USG then I'm more than happy to add that too, I just cant see what would cause this issue? Obviously I can go round removing one HA device at a time and see if that does it, or conversely add them to the BT SH2 that is currently being used as the 'switch' for the B818 network, but that only has 4 ports so can't get all the devices on it.
I can draw some diagrams if that helps!