@Mychat Was this ever resolved? I too have a new AX1500 that has worked wonderfully until the 10/28 firmware update. We have done much testing on our end and sure enough, like the OP not only is the range now limited, our WIFI drops often. My boys are back to gaming with a LAN cab;e because their wifi drops so often. I also tried downgrading to both available firmware updates and like OP, neither worked. I get the "unable to upgrade" message for both versions. 

This issue really needs to be resolved. We started having issues the night we did the firmware update. I now drop signal in what used to be the strongest parts of our house. 

@Blk00ss 

A support engineer contacted me from TP-Link to get him into a remote session so he can downgrade my firmware version, however, I am not at home where my router is installed. Gonna wait till lockdown is lifted in my area so I could fix this issue. 

I think they should look into this issue more because it's now 3 users complaining.

@Mychat Yeah, there is definitley an issue. The night my router said we had a firmware update we started seeing issues. But I thought it was just device related. As a days went on my boys started saying things like "hey is the router down? I have no wifi in my room" which has never been an issue. Then we started getting horrible lag while gaming and also started seeing drops while sitting right next to the router. All of these issues were non existent prior to the firmware update. In fact, this WAS the best router I've owned out of the 4 or 5 I've had in my lifetime.

If they don't get mine fixed I'll be pushing the store I purcahsed it from to let me return and buy a different brand. My router is only a few months old and I keep receipts on stuff like this. 

I did the live chat today with a tech. His suggestion...change the channel on both both the 2.5 5ghz channels LOL. As suspected, my issue still exists. He seemed unsure whether or not downgrading to the previous firmware was an option since it tells us "unable to upgrade". If I can't go back the to the previous firmware when the router worked great, I think I'm gonna have to return the router.

Pretty ridiculous when a firmware update kills your router in an incredibly noticeable way. This thing is night and day different from how it worked prior to the update