AX68U is rock solid and coming up to 6 days up time. NO complaints from the kids or wife unit. Thought the AX68U has never give me any problems no matter the version.
Been running the beta on the AX68U for about 4 days no problem at all and my kids haven't complained so it's rock solid in my book! Only "issue" I noticed is the web history stops recording after a few days and clearing it and rebooting the router. And it starts again.
Updated my RTAX68U FROM 388.1 to 388.2 beta 1 and so far it's flawless per normal. Updated my ac68u to ax68u last weekend and couldn't be happier! The ac68u was a great workhorse for years.