Sudden performance / blocking issues

[JustTed]

I've had Opnsense running fine for several months, connecting via PPPOE. Today, however, connectivity issues - very slow, with many websites not loading. TBH I thought it was a broadband issue, but swapping for my old Ubiquiti router has fixed it.

Tried rebooting etc, no joy. It's like some kind of TCP Clamping issue in its effect.

Any ideas or advice?