Graeme, I do not think it is weird—yet 
My previous suggestion about using 4G to bypass your router and IP number (if relevant) can also be done if you go to a friend's and use their computer, log in (or not) and see what happens (or try an equivalent scenario, like a new or different device from a café etc.)
Also if you do some changes from home, remember to trash the caches because if there is some forum server setting that is corrupted, it might be coming back each time (or randomly or whenever).
We have not got Mike to check or clean out his caches either, so he could see if this is possible (again, once done, then clear yours).
I do not know how your countries ISPs work, but it could related to the IP number coming in to the forum. If this is causing some problem, then it would explain all the devices at your house seeing the same. Take a device to a café and see what happens (clearing the cache). You could also route through one of those web proxy sites to hide or change your IP number.
Also (I know this is a long shot) log in and change your settings to US time zone (or any other) (perhaps other settings as well). Again, clear caches (including the forum server's).
And try making another new user (from the café) and see what happens with different settings than you would normally set (you might have done this when you tried this earlier).
My previous suggestion about using 4G to bypass your router and IP number (if relevant) can also be done if you go to a friend's and use their computer, log in (or not) and see what happens (or try an equivalent scenario, like a new or different device from a café etc.)
Also if you do some changes from home, remember to trash the caches because if there is some forum server setting that is corrupted, it might be coming back each time (or randomly or whenever).
We have not got Mike to check or clean out his caches either, so he could see if this is possible (again, once done, then clear yours).
I do not know how your countries ISPs work, but it could related to the IP number coming in to the forum. If this is causing some problem, then it would explain all the devices at your house seeing the same. Take a device to a café and see what happens (clearing the cache). You could also route through one of those web proxy sites to hide or change your IP number.
Also (I know this is a long shot) log in and change your settings to US time zone (or any other) (perhaps other settings as well). Again, clear caches (including the forum server's).
And try making another new user (from the café) and see what happens with different settings than you would normally set (you might have done this when you tried this earlier).