The router was connecting very well to the internet via the EE 5G network for a long time, but has suddenly stopped.  I have installed a new SIM card but this had made no difference.

According to the router admin interface, the router is running firmware build 240822, and it is telling me it wants to upgrade to build 250812

I want to upgrade the firmware to see if that will fix my connection problem, but I can't connect to the internet to do that directly.  

Therefore I need to download the firmware from the website and upgrade manually.  However, latest update published on the website is Archer NX200(EU)_V2_240822, Published Date: 2024-10-09

I cannot see anything other than beta versions of firmware shared in the this forum.
 

So, how can I either:

• A: Download firmware build 250812 
• B: Upgrade the firmware on the device without being connected to the internet

Alternatively, is there any other advice on how I address my connection problem?  It is clearly not a settings / config issue, because as I say it has been working well for several months on several EE data SIMs before this problem occurred.