I have a RB951Ui-2HnD which I have configured as a simple Home AP & router. It is connecting to a TP-Link 8817 in bridge mode.
The PPP client in the RB connects fine to the ADSL however occasionally, and usually when the link is busy (ie videos), then the PPP disconnects and the RB will then try and reconnect. The reconnect process takes minutes and often 5-10 attempts to get the connection back up. Overall in a day there

I have tested the TPLink in bridged mode to a Netgear router that I have and it remains stable for days/weeks, with no apparent disconnects. And the Netgear on it's own (it also has an ADSL modem) is fine for days/weeks too.

I'm at a loss as to which settings I should be looking at or tweaking. Any ideas please?

Did you every discover a solution to this, I am experiencing the same thing with a hex lite and a tp-link 8960N in bridge mode. 5-10 disconnections per day. Modem doesn't drop sync it's the pppoe on the router.

Unfortunately not, I still get the issue. Some days it's bad, and some days I can be up for a whole day.

I have quite a few RB951's deployed with ECI B-Focus and Huawei HG612 DSL modems, with PPPoE being initiated from the Routerboard. I do not see the kind of behaviour you're describing. Not much help to you, I know.

I think your best bet is to turn up the logging and take it from there.

I'm coming to the opinion that it's related to my filter or cabling. Am in the process of swapping components out to isolate it.

in case this helps, i had the same problem. i think i fixe it by setting the mtu and max mtu values on my ether1 physical wan interface to match the pppoe virtual interface (my isp advised 1492) and the problem went away