One thing to note is that @batkung is on a 1900acs, which does use a different WiFi chip than the 3200acm/32x. It seems like the 3200acm/32x are the main units to be effected by dropouts, per this thread: Users needed to test Wi-Fi stability on Linksys WRT3200ACM & WRT32X on OpenWrt 21.02.0-rc4
BUT, there is at least one report of a 1900acs having the same issue, so it's a roll of the dice at this point - Users needed to test Wi-Fi stability on Linksys WRT3200ACM & WRT32X on OpenWrt 21.02.0-rc4 - #90 by petersmith