I understand your frustration. I have not used mobile broadband for gaming, yet.. If i do decide to cancel my ADSL in favour of mobile then i'm sure the same issue you're having will rear its ugly head with me.
I am not well versed in nat types and the such to give you a definite answer to your question, only what i've read on other forums these past few days. It most likely does have something to do with your ip and whether you use a shared ip at the carrier side. Whether EE will have a fix for that issue, i'm not sure.
My advice would be to contact using their phone service and ask for technical help and hope you get someone who knows what you're talking about. If that fails, perhaps complaining to higher management via email and type up a firm but polite email in hopes for a fix.
https://community.ee.co.uk/t5/4GEE-WiFi/Public-Ip-ad...
I done a bit of googling while writing this and most of what i've seen tells the same story. I don't think you're going to get the public/static ip you need, not from EE anyway.
I think you'll have to try your luck with three or another provider. I may be wrong on this too but i think three offer 100gb data sims (not mobile sim plans) in store.
Take what i say as a pinch of salt though.
With a bit more reading i've found that people use the service from
https://www.noip.com/ to sort similar issues. I have no idea how it works though. Perhaps others on the forum could give you a step by step guide on how to apply everything on your end after trialing the service.
Michael.
Edited by deleted (Fri 12-Oct-18 19:21:42)