Could you call to your SIM operator asking about status of 4G in your line? I has this problem, and my surprise service 4G was disabled. Operator actived it, and after restarted my Iron 4G working ok
I think there are a hardware or software problem (IronPro or romV3.02)
Any 4G SIM working OK into other phone.
When you put it into Iron, work OK...
...but when you removed it, the 4G service is disabled to this line!!!
I will try to call my phone operator , to see if I have this part of 4g disabled , you know something I do not like is that if another company has 4g signal but not mine , I will be calling to see who can find