It's interesting that it reports invalid key, because it should report invalid passphrase. Otherwise it's not the eureka moment we are seeking. The \ character is not an allowed character for passphrases and is thus rejected, end of story.
The 'invalid-key' other folks are seeing is a crypto key being exchanged between client and access-point, and it's deep in the guts of the negotiations needed for some radio features. Weak signals tend to surface it more, which suggests it's related to error handling (or not-handling) code somewhere in the wireless stack. It also shows up with Broadcom WiFi hardware and WPA3 which is not fully supported in current kernel drivers for that hardware; although we've applied mitigations for that now.
I've removed "[SOLVED]" from the thread title because I don't want the noise of others pointing out that "there's a solution you're not telling us about" and/or that your solution doesn't work for them.