EC25-V Verizon Connection Issues, how to dignose?

I have multiple, identical openwrt-devices, originally equipped with EC25-V. Even, in case positioned side-by-side, some devices connect immediately to Verizon, some of them only after few hours, using PPPD. Any hints, how to track down the issue ? SIM is not the issue, exchange between “Good” and “Bad” device does not change behaviour.

Hello there
If there is no change after you exchange the device, we suggest you check the state of your “bad” device, if the PPPD work after several hours, maybe the register network has problem. Please check the antenna connect well and retry, thank you.