NR5103E with Firmware: V1.00(ACBJ.0)b14 no 5G connection

[cc-1]

I've got the NR5103E with Firmware: V1.00(ACBJ.0)b14 and get no 5G connection whatsoever.

I've had Three replace both the sim and the router and this has not resolved the problem.

Putting the sim into an iPhone 13 gives 5G connection in the same room as the router.

I have excellent signal strength at -91. Router states access via LTE-A.

All settings on the router as as supplied, e.g. cellular band NR5G-NSA/4G (Auto Switch).

Previously I seem to remember being on the b12 Firmware and before that I had the Huawei 5G CPE Pro - both of these devices connected to 5G with no problem.

Any suggestions on what can fix this problem?

[cc-1]

Firmware updated to V1.00(ACBJ.0)b15 - now I regularly get 5G connection but it is very unstable and the connection speed is slower than the 4G connection speed. Appears to be a firmware problem as this is the only variable.