DD-WRT seems to have fixed the bug with ESP devices not connecting to ATH1 on a WRT32X - presumably with a driver update. Has the same update been applied in Openwrt?
Do you have a specific patch that was used there?
One thing I found in my notes is that
should enable 802.11n mode for at least an ESP8266 (in its source)
not sure (sorry I find the dd-wrt file system very difficult to follow compared to openwrt) but it didn't work until the release issued 26th March. From memory there's a command to check the mwlwifi version but I cant for the life of me remember how to do it.
I don't see anything recent in the commit messages from the DD-WRT git mirror
Most recent commit that matches "mwl" is (note that is 2018, not 2019)
commit b512e8ee597 Author: BrainSlayer <firstname.lastname@example.org> Date: Sun Mar 25 13:59:20 2018 +0000 disable for mwlwifi, the binary firmware seem to block these frames
(I did double check, and the mirror looks to be up to date, with the latest commit on Wed Mar 27 01:59:58 2019 +0000)