Another test: I tried grounding my sled with a copper wire:
The wire is attached to the sled with 4 self tapping screws and runs across the plexiglass cover and is wrapped around the dust collector. It is connected to mains ground using a standard mains plug (don’t worry about the blue and brown wires, they are both connected to the ground/earth pin).
I ran the same test cut that had always failed, but now it succeeded (I ran the test 4 times, router cutting and dust collection on).
BTW, I also replaced the standard CAT6 cables with longer ones (50 cm). I think the standard cables are a bit short and rigid, causing the RJ45 connectors to wiggle in their sockets when the motor arms are rotating.
With the longer cables, the connectors move a lot less and I haven’t seen anymore connection problems.