WDR3600: ath79 19.07.3 Wifi 2.4 GHz fails after a few days

I have three TP Link WDR3600 routers mainly for Wifi access. These have been running 18.06.4 for a few years with no problems. Recently I upgraded them to 19.07.3 the ath79 default version. Since then the 2.4 GHz Wifi stops working after a few days. The Wifi is up and seen by devices, but devices can't fully connect. They appear to connect at the Wifi level but fail when getting the IP address. DHCP is done by a separate DHCP server and when this problem happens you can connect to the routers 5 GHz Wifi fine.
I do see some syslog messages indicating an error with WPA occasionally (should have noted these ...) Rebooting the routers clears the problem.
I have moved one back to 18.06.4 and moved another to 19.0.3 the ar71xx version to see how they behave.
Anyone else having problems with 19.07.3 2.4 GHz Wifi on WDR3600/WDR4300 ?

I have moved back to 18.06.04 one one router and this seems fine.
I also moved a router to the 19.0.3 the ar71xx version and this seems fine.
So there appears to be an issue with the ath79 port.

I've started (actively) using my tl-wdr3600 again about two months ago, running an irregularly updated ath79 master snapshot - it's been fine so far.

30 days uptime since last reboot and the wifi work fine, dhcp server is on the same device.

TP-Link TL-WDR3600 v1
19.07.3 r11063-85e04e9f46

Thanks for the feedback. The two TP-Link TL-WDR3600 v1 routes have been running for 9 days using the 19.0.3 the ar71xx version. Following the feedback, I will move these back to the 19.07.3 the ath79 default version and try again...

My WDR4300 has been running 19.07.3 with the default ath79 drivers since the release, without any issue so far.

19.0 both ar71xx and ath79 had problems with random packet loss on Wifi 2.4ghz. Wifi 5 ghz has very low signal-range to be operational. 18.06 version seems more stable.
Also which of the chips does your device have AR5980 or AR5982, could that be an issue?
Mine has the first one.

I have wdr3600 (ath79 19.07.5) and I think have same fails.
do you use it as a repeater?
Do you use wds or relayd or mesh?

I use the two radios as a repeater (relay bridge), 2.4Ghz as wlan (AP mode) and 5Ghz as wwan (STA mode).

i' ve been using the wdr3600 as an ap. Low wifi 5 ghz was fixed after loading stock firmware and then openwrt 18. again. But packet loss comes up randomly in a period of 1-4 days. I usually notice the packet loss during a teleconference. Out of ideas, thinking of trying a new router. There are many similar reports posted like WiFi on WDR3600 unstable after 2-3 Days