WiFi Problem on Raspberry Pi

Raspberry Pi 4B 4GB has operated a very conventional x,y,z mill with a Mesa 7i96 for a couple of years.
WiFi never worked and has been a back-burner issue for a year or more.

Two cubicles:
 - Power: VFD, stepper supply, general supplies, AC/DC relays,
 - Electronics: RPi, stepper drivers, DC relays, power supplies,
     - minimal 240VAC cabling for power supplies, monitor.
 Monitor, keyboard and mouse cabled.

WiFi-Extender for workshop 4m from RPi.
Test set-up on workshop bench 6m from Extender.
Bench desktop ethernet cabled to extender, has always had reliable WiFi.

I have two RPi; 4GB and 8GB.
The 4GB is currently LC2.9.2, and I downloaded LC2.9.4 recently to a separate SD card.

Investigated:
 - both 4GB and 8GB operate WiFi with either L2.9.2 or LC2.9.4 on the bench no problem,
 - confirmed linked to the Extender by switching it Off (house WiFi 5G is at -70dBm),
 - both operated with Mesa card Off,
 - both fail to launch WiFi in electronic cubicle when mounted or hung in free space.

Also:
 - both have identical (as close as I can tell) WiFi set-up,
 - both detect the Extender and show signal level at -40dBm,
 - both fail to scan for ssid using menu-config in LC2.9.4,
 - both respond to "iw dev wlan0 scan" with response for Extender at -40dBm.

Note: test in cubicle has all non-essential supplies Off: VFD, steppers, Mesa, general control,
nothing else in workshop energised, other than air conditioner and desktop.

Need suggestions on which stone to turn over next.
John.

Try 2.4 GHz. 5 GHz is not as reliable in an industrial setting and has much shorter range. I turned off all my 5G wifi

Failing that use a wifi USB dongle that has an external antenna and get a SMA bulkhead mount cable to extend it outside of the cabinet

Thanks Rod, the external antenna was my next move.
I am in Sydney, any suggestion on model number that is known to work with LC2.9.4 ?

The Extender has been set up to use 2.4 GHz from the start.

The engineer in me wants to know why the failure in the cubicle.
I will do some more testing.
John.

What material is the enclosure ?

Steel, 400 x 600 x 190.
See attached (poor) photo showing RPi hanging in space:
Row 1: stepper drivers,
Row 2: RPi stacked on Mesa, I/O PSU,
Row 3: 12 Vdc relays, Mesa core PSU,
Row 4: Terminals,
Side: stepper sockets, hole for monitor+keyboard+mouse cables, GPO for monitor + RPi.
Terminals and cables as appropriate, much neater generally.

I have a virtually identical cubicle with some electrical equipment in it.
Stripping and testing should begin next week.

The RPi 4GB and L2.9.2 need to go back to their day job of cutting metal.
John.

A grounded steel enclosure is not the best place to be emitting radio signals from.

Nowadays just about any wifi dongle will work, but it will need an external antennae.

Should a good starting point for usable wifi adapters, anything that works with Debian Bookworm will work.
github.com/morrownr/USB-WiFi

If you need extra help I'm located in Sydney as well.