@Hiccups Sadly, I have the V3 router, so there's no firmware to downgrade to. Idk if the V2 firmware would work, but better not brick the device. It really is a firmware issue, I regret buying this router :(

  As @Sporall reported I back revd to 1.6.0 0.9.1 and now get a constant 4g+:

But despite on most occasions getting a carrie (EE) next to the associated bands

It doesnt display the bands correctly:

Occasionally when having 3 and 20 selected it shows 3,3 and others just 3.

@Sunshine 
I have the same issue in India with jio carrier on my Archer MR600 V3.

The thing is Jio supports two band combinations:

1. B3,B5
2. B40,B40

I tried B3, and B5 combinations which didn't work and I can't even try B40, and B40 combinations since the UI is not allowing me.
 

I've been scouring the internet for the past 6 hours, and now I stumble upon this thread.

It's beyond maddening! These marketing people at TP-Link are a bunch of charlatans.
They hype up their products like they're some kind of god-mode solution, but in reality, it's all smoke and mirrors.
There are so many damn ifs and buts!
 

I shelled out a small fortune for this piece of junk, and now I feel like a total sucker.

I could have easily bought a 1500rs 4G USB modem, slapped it onto a mobile adapter, and called it a day.

Why the hell did I waste more than 8000 RS on this device if it only supports one stinking band?
 

And don't even get me started on TP-Link's incompetence.
I'm a software developer, and I can tell you, it's not just that they're lying in their marketing; it's that they couldn't care less about fixing this issue!
This problem has been plaguing us for the last 3 agonizing years, and what have they done about it?

Absolutely NOTHING!

 

TP-Link, you should be ashamed of yourselves.

Your entire department needs to be axed for not giving a damn about resolving this issue which is Core Feature Of Your Device and has been tormenting us for THREE LONG YEARS!

How can you be so slow and indifferent to your customers' suffering?
It's infuriating beyond words! 😡🤬🤯

I'm tempted to approach trading standards.

This router is still listed by TP link as a 4g+ router, which it clearly isn't.

I think I'll write to them first to give them a chance to resolve it, but otherwise there are a lot of other people who've purchased this since the issue started who probably don't even realise they're not getting what is advertised.

  @Sunshine This is beyond ridiculous, they don't update the V3 firmware and don't fix the 4G+ issues. My router decides to lose a band one day, the other day it detects it again, some days "no available band" but immediately after a restart it detects them. This router is really bad and their service is terrible. More and more people have this issue and they do nothing about it. A 4G+ router filled with bugs and riddled with bad firmware and TP-Link does nothing. I'm not going to buy anything from them anymore.

  @Sunshine I'm not emailing anyone, after your "support engineers" all they do is basic testing, restarting the router, common things us folk have DONE ALREADY for the past three years. It's like talking to a wall.

I'm a literal Software Engineer, and the issue is with the router's firmware, it's bad programming on your part, and it's a terrible product.
Copying and pasting this really pathetic answer and masquerading it as some sort of "solution" is exactly why no one else should buy your horrible products.

All you needed to do was update the firmware for all models of the MR600 and actually understand the issue is on YOUR SIDE. Stop asking people to do basic testing like we're babies, it's shameful and disgraceful, and I wish I didn't give this company a single dime.

  @Sunshine 

As already stated and correctly so by members on this forum this firmware issue has going on for 3 years with no end in site . The MR600 from V1 to V3 suffers from this intermittant carrier aggregation issue. If you are like me with a V1 with its multitude of beta fixes to correct errors like sms messages not displaying and many other issues and  after a major beta fix last year in September is still running on beta firmware and wondering whether there will ever be an official version. To go back to the buggy official last release  is not an option as it introduces a whole lot other errors. Its time for this issue to be resolved and I don't blame customers that are starting to  use aggressive language. You asked for a name of a router that works properly with carrier aggregation . Here is one its an Huawei B535_235F which works as it should. No beta versions firmware, only official released and working. What I don't understand is why your software engineers cannot sort this out. Logs submitted show the 2 second switching between LTE/LTE + . If you can't sort out carrier aggregation on these units then community stay clear of any proposed  5G units when they are released.