If you remember I had constricted a bridge from wifi to ethernet to act
as a bridged access point. On a PI 4B as a test platform

The problem was that whilst the bridge was reasonably OK accessing my
LAN, up to 90% packet loss was experienced when accessing the internet
via my edge router.

Two further points have been established but the exact reason for the behaviour still remains a mystery

1/. A friend with a Pi 5 attempted to duplicate the setup, could not get
it to work and instead used the Network Manager GUI to set up a
(routed?) access point which worked ok. It turns out that you cannot use
the GUI tool to set up a bridge at all. Only nmcli.

2/. After a long time with traceroutes and pings I realised that this particular machine was the *only one wired directly to the router via a
single gigabit Ethernet cable*. Everything else went via an ancient
100Mbps switch that I inherited from an office clearout. In a rash of
'well I tried everything else' I unplugged the Pi from the Gigabit
router socket and put it into the 100Mbps switch and bingo!... Pretty
decent internet performance. Yes extremely long transfers sometimes
fail, but its very useable

What I cannot for the life of me understand is *why* this worked. The
same [Gigabit] link was involved in both local and Internet access. The
only difference being that local access ALSO went through a 100Mbps switch.

If anyone can shed light on this I would appreciate it.

If it matters, the router is a Draytek Vigor2762Vac running PPPoE via an Openrach ONT to an optical fibre for Internet and thence to the ISP.

--
Socialism is the philosophy of failure, the creed of ignorance and the
gospel of envy.

Its inherent virtue is the equal sharing of misery.

Winston Churchill


--- PyGate Linux v1.5.11
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)