I was doing some testing today, and had the RPi4B sitting on a metal surface. It was only about a metre from my Nexus DSC, and it refused to connect. (RPi as client)
It was showing full strength signal from the Nexus, but wouldnt log-on. Went in a loop keep asking for password and then it gave up.
Tried it with some other wifi sources - all the same.
Tried another RPi, identical problem.
Both had previously connected to the Nexus countless times.
Moved the RPi off the metal surface - instant connection.
The metal surface wasnt in-between the RPi & wifi source. The Pi is in a plastic case and just within about 5-8mm of the metal surface and the Nexus was way above the surface. The metal surface wasnt grounded.
I know the RPi wifi antenna is 'pants' and I usually only rely on 2-3m range. But this behaviour was a bit of a surprise (and explains a few things!)
Mounting a RPi on a metal telescope may degrade the wifi more than you would expect, even though it looks like full strength.