Just had an interesting update from Ubiquiti:
Hi There,
I appreciate your patience,
The development team was able to reproduce the issues that you're experiencing on the primary WAN (port 19). They are working on a resolution. I'll reach out when I have an update from the development team.
Best,
UI Support
Ubiquiti Inc.
I can replicate the issue on a UDM-SE and UDW on the 2.5GbE port by completely saturating a 1Gb connection and a PPPoE connection randomly dies. If the test is repeated using the SFP+ interface, using the same download test it works fine. I had to do some testing for them which I have forwarded over as I was running a tail and top on the unit in question. I am happy they can re-create it though, so that's one positive.
Wonder if they will release a new firmware for it?