@Shanmu
I have bought MR400 and been faced with "lte connection disconnected" issue in the log. Wi-Fi was connected but there is a drop in internet and it comes back. I am using it for work. I was mostly on MS team where it is annoying for everyone and my work vpn / VDI was frequently disconnecting. I was searching all over the forum and found that it is the Band change that causes the issue.
If it changes from Band 3 to Band 20 or Band 40 then there is a drop. So, I have moved around the router at my home where I get Band 40 constantly.
Band 3 - Low speed, good signal Strength
Band 20 - Moderate Speed, Moderate or good Signal Strength
Band 40 - High Speed, less Signal Strength.
The Band defines the frequency of the cell signal, low hertz will travel a long distance but slower data speed.
If still you have issues there is Beta firmware for the MR200, MR400 and MR600 (one beta Firmware) from this link
https://community.tp-link.com/en/home/forum/topic/222354
you can upgrade to beta firmware and I think you have option to choose a Band and force the router not to change the band.