Users having issues connecting

[BNSL BobbyS]

A couple users are having problems connecting to our forums, but only from specific devices/locations.  It basically times out, saying the server is not (has stopped) responding. 

I've contacted cloud support to make sure their IP addresses weren't banned, and they said there are no problems on that end. 

One cannot get through via his Mobile connection (he can get on when connected through Wi-Fi though) with AT&T LTE. The other cannot get through from his home network, but can from work. So it's not a username issue, either. 

They have tried the usual resets, history/data/etc clearing and the sort. 

Just curious if anybody might have any ideas as to what the issue could be, and perhaps how to solve it for them. 

Thanks!