I recently bought a AR750s-ext and was suffering the same wifi disconnects as described above, I tried a number of solutions which worked for a while and then…

I am connected to a hotel hotspot normally, i have tried multiple hotspots some were better than others…

My solution has turned out to be quite simple:
For information it may not work for everyone but after researching it appears to work so far on all connections.

Clone the MAC address to a Laptop or smartphone etc, the newer hotspotsor their ISPs are blocking MAC addresses related to router suppliers.

It’s just information and I hope it helps others.