@svanheule I've built your tplink_eap2x5 branch and attempted to install it on my EAP 225 Outdoor v1. I first ran cliclientd stopcs as you suggested in your released firmware image. When I attempted to install the (renamed) openwrt-ath79-generic-tplink_eap225-outdoor-v1-squashfs-factory.bin file I received back a "Bad file." error.
My unit is currently running 1.20.0 Build 20200604 Rel. 51951(5553) which is a Canadian firmware file available here: https://www.tp-link.com/ca/support/download/eap225-outdoor/#Firmware.
Please let me know if there's anything I can do to help test the cause of this issue. I'm online on freenode as johnf and asked you about this release a few days ago if you prefer to chat, I'll update this thread with any interesting information.