There is known, recurring, frustrating, fault with the H3G core they refuse to fix. I have a 3 unlimited SIM in a Draytek 2860Ln. I’m only about 500m line of sight across an open field from the 3 tower (I could actually sling a wire to it!) so RAN connection/signal is not issue. DL peaks up to 120Mb with 30Mb UL. All good so far. However, the issue is an ongoing KNOWN packet loss issue. Changing DNS, MTU, band, access tech (3G/4G) make little difference. However, using a VPN almost completely eliminates the problem.

I wrote an app to hit a list of 10 URLs every minute. At worst, I see over 25% failure with an average of 9-10%. It's a consistent packet loss issue. To compare, EE MBB shows less than 0.05%. There must be a serious flaw in the 3 core.

Many calls to 1st and 2nd line get 'we don’t know how it works’, ‘we can do nothing about it’ and ‘would you like to cancel?’ responses. It’s as though they view their core as some sort of magic they won’t question. Escalation requests are get 'I don’t know how to do that’ or ‘we are not allowed to do that'. They DO NOT DESERVE TO BE IN BUSINESS with that attitude. I stated MANY report the same thing, country-wide, but with no interest.

Tip - use ‘3internet’ as the APN, you get a dynamic public IP, that u can use with a DDNS service.
reached 1400 limit - See my posts in forums for more.