@TBinsx1  hello, I request you to visit this page.

https://community.tp-link.com/en/home/forum/topic/521384?page=1

  @Namann1 

Hi. Thank for the hint.

I've visuted the link but the problem, and device too, is different

  @TP-Link 

Here attached a screenshot. There are no other sign/messages than stopping of down data flow (it also indicates 0 bps).

I've updated the firmware and also tried locking operation in 3G (their standard) but the problem remains.

I've two SIMs from the same operator and I tried swaping them:  the problem is showing with only one, the latest I bought.  When inserted in the smartphone, both SIM are working perfectly (as in the midem, apart the stopping after had paused browsing)

I've contacted the operator discussing the problem and the only hint was to try replacing -by paying- the SIM.  I didn't agree and I will now try to insert "that" SIM into another smartphone acting as hotspot but, I'm afraid the Android o.s. will, somehow, keep the download line alive, making the test unreliable.

Intriguing problem, isn't it?!

  @TP-Link 

Hi, I still have the problem on two MR6400 (in the meantime I bought another ...) and I discovered another user has the same problem.

Since I first thought it was a problem of ISP, cooperating with them, I can exclude problem on their side. I've, contrarily, focused precisely the situation the generates the problem: it happens just when to modem are connected smartphone (Android) or Linux PC - not happening when Windows PC is connected.  In fact, when one Linux/Android device is connected and, due to reading a long doc/page, the communication does not generate data flow, the model "stalls" and sometimes return alive in 30-60sec, sometime it does not get back.
Windows is always generating data flow (150bps minimum) due to continuous calls to Microsoft server, that keep communication alive.

WHAT can I do?

Firmware check:

Device Information

Firmware Version: 1.10.0 0.9.1 v0001.0 Build 190521 Rel.38696n

Hardware Version: TL-MR6400 v4 00000001

Online Upgrade

Latest Version: 1.10.0 0.9.1 v0001.0 Build 190521 Rel.38696n 

... Your firmware is up to date