@Itsuki 

Hi, thank you very much for the feedback. Please help to confirm the following information:

1. Please make sure external antennas are installed properly

2. If you change the Network Mode from 4G Only to 4G Prefered, change Band back to Auto, will it work with SIM card 3? If so, please check Network Type on Status page to see if it is WCDMA or LTE

3. If you insert the same SIM card 3 into another 4G device or smart phone, will it work on 4G network? If so, are you able to check which 4G band it works on?

  @Itsuki 

Hi, for the point 3, if the same SIM card works fine on another device at same location, please help to check the network type and band working on that device.

If you tested it on a smartphone only, for android phone, you could install LTE Discovery App or LTE Cell Info: Network Status App etc. to check the network type and band.
For iPhone, please type *3001#12345#* into the area you normally use to input a phone number and press call. You will enter Field Test mode, and you should see the Freq Band Indicator or EARFCN or UARFCN number.