Hi, looking for some help please.

We moved to a rural area with poor broadband speed. I opted for a 4g router system. We have a TPLINK MR600 with an external antenna, running on EE. I set this up in October 2021 and we have been running perfect with consistent speed of around 40mb. 
 

This week the connection has become really temperamental with the speed keep dropping to 2mb and sometimes going back up. If I reboot the router that sometimes helps. If I speed test it might show a download speed of 25mb but the connection is still slow?? 

I have checked all connections and running on the last way firmware. 
 

Does anyone have any ideas that could help?