@NARESH_GURJAR 

Hi, thank you for posting on TP-Link Community.

1. Are you using auto LTE band or manually selected band? Please share with us screenshots of Advanced->Status page and Advanced->Network->Internet page.

2. Please insert the same VI SIM into your smartphone and check if the phone is always on 4G+ at same location, if so, please let us know the brand and model of your phone, also share with us screenshots of band info on the phone as well: How to check the 4G band working on our smartphones

3. If you run speedtest or download large files on the client devices, will the router switch to 4G+ automatically?

4. Please share with us a system log file saved on Advanced->System Tools->System Log page.

5. Please provide complete firmware version including the build numbers.

  @NARESH_GURJAR 

Hi, I don't see the system log file, could you please attach it again?

Besides, you mentioned that your vivo phone vivo917 is not on 4G+ all the time with the same VI SIM, actually whether it works on 4G+ is usually decided by the ISP base station, we are not able to force it on 4G+, so does the MR600. 

If your phone is mostly on 4G+, please still help to check the band on the phone when it uses 4G+, we need to confirm if it uses band 1 and band 3, since you selected band 1 and 3 manually on the MR600.