Have you noticed that if you uncheck remote http acces(cgi-bin/luci/admin/system/admin/access_control) and don't have any firewall rules enabled or added to overcome that(RMS disabeled). <<<< this policy don't work you can access any device anywhere remotely.
I have same 4G SIM provider (RUT and phone) and i can't access remotely anywhere but if i use my phone random WiFi network then i can (any other 4G SIM provider and it works).
VPN IPSEC same issue if my devices use same 4G SIM card then client can't connect! To overcome that i have to first connect random WiFI then i can connect VPN (another 4G provider works without WiFi)
last 4 FW same issue - older ones i don't remember..
4G SIM = Tele2 EE