Mobile network data issues

[Joshrog5]

Please tell us some basic information before asking for help:
Model Name: ROG Phone 5, ASUS_I005DA, EU_I005D
Firmware Version:
Rooted or not: Not
Frequency of Occurrence: Constant
APP Name & APP Version (If your issue relates to the app):
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Just got this phone the other day from the ASUS UK web store. Have been unable to maintain a constant mobile data connection at all. I've tried both with an EE sim and a Three sim, both sims work perfectly in other phones (Pixel 4 & Pixel 2 XL) with full 4G reception.
I'll get maybe a bar or 2 of 4G connection, and maybe a few seconds of semi-working mobile data before I get the "No internet" status, usually followed by the the the connection dropping down to 3G then EDGE (2G) shortly after, which don't seem to work either.
Looking at the network in settings it often seems to be Disconnected instead of the correct network. Switching to manually choose a network will often simply fail, stating the network service is unavailable. If it does successfully connect the issues stated above still occur. In the menu to select the network I can see both the 4G and Edge networks at are full or near to full reception but when I connect to them I never get that high reception.
I've tried changing APNs various times to a multitude of a different values (including the officials ones suggested by EE and Three) to no success.
I've tried both sim slots for all of this, no success either.
I've run some of the relevant tests via the calculator app:
Sim Card Test: Pass
Sim Card2 Test: Pass
Sim Signal Test: Fail (Success button never appears) I'll see various things here as the mobile work connection changes: Both connected and disconnected network. Edge signal strength: 11(asu), -91(dBm), LTE signal strength: 20 (asu) -210 (dBm), LTE signal strength: -2147383509 (asu) 2147383647 (dBm). Similar signal strenth results for HSPAP.
 
Looking around the forum this worryingly seems to be a somewhat common issue with other Asus phones. In particular this thread seems to suggest that a recent software update broke the phone's support for the EE network, and that the only confirmed way for me to fix the problem is to get a Vodafone sim. https://zentalk.asus.com/en/discussion/42198/update-17-0823-2009-99-broke-moblie-internet

[Anders_ASUS]

waxy78611

https://zentalk.asus.com/en/discussion/comment/165958#Comment_165958

Ah you have the issue too bud. Android system shouldn't be that high up. It should be much lower. The Rog 2 had same issue and Asus fixed it with a update. Android System should be way lower down on the list for battery usage.

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I will check with my colleagues in Taiwan if they've had any complaints about battery drain. If not, then I will need a log from your device. I'll get back to you once I know

[waxy78611]

Anders_ASUS

https://zentalk.asus.com/en/discussion/comment/165960#Comment_165960

I will check with my colleagues in Taiwan if they've had any complaints about battery drain. If not, then I will need a log from your device. I'll get back to you once I know

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And what about volte ??
Every single smartphone has volte and has done For the past few years. Every year whenever Asus launch a phone, they mention the volte feature. But why doesn't this feature work? How can you screw up such a basic capability which every other phone has 4 years in a Row? Why lie and promote volte when you don't bother to even make it work?

[Anders_ASUS]

waxy78611

https://zentalk.asus.com/en/discussion/comment/166280#Comment_166280

And what about volte ??

Every single smartphone has volte and has done For the past few years. Every year whenever Asus launch a phone, they mention the volte feature. But why doesn't this feature work? How can you screw up such a basic capability which every other phone has 4 years in a Row? Why lie and promote volte when you don't bother to even make it work?

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VoLTE is enabled model by model and carrier by carrier. We're not promoting that this feature works everywhere.
If ROG 5 is officially sold in your country (not by grey import) then you're welcome to contact your local ASUS and ask why your carrier is still not supported for VoLTE. It's the responsibility of the local offices to make sure VoLTE works for their carriers (but only if they're selling this product).

[Joshrog5]

So I was pretty convinced this was a hardware problem and that I'd need to get the phone replaced. HOWEVER I got my vodaphone SIM card today, put it in and IT WORKS PERFECTLY. Am writing this on a full 4G connection right now.
Super super strange, so I guess maybe this is a software issue? Or a hardware issue that only effects certain SIM types? No idea honestly but happy to have a working phone again at least.

(I actually got an Asda SIM since they switched to the Vodafone network earlier this year and don't require year+ long contracts)