Sorry you're still having issues. All my PCs have an Ethernet cable directly connected to the router so I'm not sure how the router responds to wireless connections with this problem. Unfortunately, I can only tell you how I was able to fix the issue...
Yes, it was locking up after 10 minutes, not rebooting. The first time I rebooted, the router locked up before I could start the firmware download. The second time I log in right away and started the firmware download as quickly as I could and it do...
Like @b4evrtru26 mentioned, do a hard reboot of the router. That should give you time to connect to the router via gui and download the firmware. That's how I did it. It took me a couple times, but I finally got it downloaded.
This beta firmware got my router up and running. RT-AX89U_9.0.0.4_388_32094-ge476ac0_for_user.trx . I can't post a url for some reason so you'll have to google it.
