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Yeah, I thought it might be something to do with the php session. Is there any workaround or setting I can change? Thanks.

I'm not, it goes to the login screen and doesn't display the above error.

I've done a few experiments in FireFox and the login and logout work fine. Just seems to be Safari and Edge that have this problem.

I've cleared the cache and history in Safari but it still does the same thing.

There is an error message behind that box but I can't see what it is as it reappears so quickly.

I set a value of 60 but there's no difference. As soon as I click logout I'm stuck with this screen. Clicking refresh just gives me this screen again.

This only happens when you try to log out.

The inactivity timeout is set at zero.

Yeah, just discovered if you leave the 'Branding -> Welcome Message' blank then nothing appears. 

Sorry, I meant the message box that appears just after you've logged in.

Hi Vlad, I got to the bottom of it. I was clicking the little edit icon, filling in my tags and then not clicking the little 'disk' save icon to save them. My fault, apologies and thanks for your patience.