Ignore it anyway, it on a second look wouldn't be stopping you anyway. My last suggestion that is.

@Mslav Only other thing that springs to mind is you have AP isolation switched on on the main network and not of the guest.

I think I know what is happening and it's simple. You need to enable the wifi from the webpage 192 ... ... ... and save it, I'm pretty sure what is happening is you have the router set to off at some...

New FW out now for the V3 anyway and I thought this one had gone EOL, good job TPL.

@Gastomagic Turn off SIP ALG in ALG settings in securoity tab. There is also another reason this happens, wifi interference, is the microwave in use when it happens?

@Cadiper Check your blacklist/whitelist settings incase you've unintentionally added them to a whitelist and accidently turned the balcklisting on, assuming you use that function.