Is mine and I've tried all the above. There's no firmware upgrades for TP-MR6400 v2 on tplink.. I've done factory resets, trying out different locations, etc, nothing. I live in the capital of the country and I've tried it in two different areas of the city (one of them is city center), all around the rooms of both places, on multiple devices, different OSes (android, ios, windows, mac) and I use the same SIM provider (one of the country's widest covered providers) with a similar package I use on my mobile phone SIM - mobile phone works perfectly. I need to create a mobile hotspot so we can use the laptop, tv and other wifi connected devices (same ones that fail on the TL-MR6400) without problems. So this is clearly a TL-MR6400 issue, not something else.

It is completely unreliable for downloading anything remotely larger, having a stable internet connection over a longer period of time or, for example, attempting to stream netflix on a large TV (just doesn't manage to finish starting the video). Currently, my large screen TV is connected to my mobile phone's hotspot when we watch Netflix for example, as router is completely unusable, both wireless and wired (this isn't just a wireless thing).

This issue has been ongoing pretty much since I bought this around 2 years ago, I should've done more research as there's a lot of complaints elsewhere as well and no concrete solutions. Really regretting this purchase.

My recommendation to anyone googling reviews for TP-LINK TP-MR6400 (or currently any tp-link product): Avoid at all costs.