Hmm well, in my experience (not just with Canon) if there is any issue that is remotely obscure, the front line support staff will not really know if something like that is or isn’t a hardware issue. I mean, it might be but personally I'd try and rule out as many other possibilities first and showing it's somehow related to wifi is a great first step.
Have you used your phone to connect to the camera while you were playing before this started happening? If so, can you bring up the wifi settings, see if the R5 wifi is listed and if it changes to connected when this happens? If so, out of interest do you have the wifi password saved in the wifi settings? If I try to force my phone to join the network just in wifi settings, then it pops up asking for a password, if I use the app, it is like that supplies the password rather than saving it in the wifi settings i.e. so my phone is not able to actually connect unless the app tries to initiate it. I am wondering if the password was actually saved in the wifi settings, the phone might be connecting and authenticating over wifi and causing the issue, thinking your camera is a wifi access point briefly until it realises there is no internet gateway, if that was the case you could try selecting “Forget this network” in the settings.
I would certainly be trying to confirm there is something actually trying to connect to your camera that is causing it.
You could also try clearing out any info related to your camera from your phone and also if that doesn't help, reset your camera to factory settings to start afresh before resorting to sending it in if you're already outside the 14 day window.