WiFi connection lost every ~2 minutes immediately after updating to 2.2.1(5)

Hello,

I have an OpenSprinkler v3.x controller that became unable to hold a WiFi
connection immediately after the firmware update to 2.2.1(5). I would like to
ask whether this is a known regression, and whether an older build is available.

TIMELINE

13 Aug 2026, 05:08:40 controller rebooted, reboot cause “firmware update”
13 Aug 2026, 05:14:23 first WiFi disconnect

That is 5 minutes 43 seconds after the update. In the 8 days before the update
there was not a single disconnect. In the ~30 hours after it, there were 37.
The controller has been reassociating roughly every 1-2 minutes ever since.

MEASUREMENTS (taken from the access point, not from the controller)

Signal -75 to -77 dBm, noise floor -96 dBm
TX retry rate 63% (137 of 218 frames), later 49% after I changed channels
Reassociation every 60-120 seconds, continuously
Negotiated rate pinned at the minimum allowed by the SSID

THE PART I CANNOT EXPLAIN

The controller sits about 1 metre from a WiFi 6/7 access point (Ubiquiti U7),
and roughly two rooms away from an older WiFi 5 access point. It connects only
to the distant WiFi 5 unit, at -76 dBm, and never to the one 1 metre away.

When I configured the network so that the nearby access point was the only one
it was allowed to use, the controller did not connect to it at all – it stayed
completely offline for the full 6 minutes of the test, then recovered as soon
as the distant access point was permitted again. This is reproducible.

A cold power cycle does not change the behaviour: after a full rescan it still
selects the distant access point.

WHAT I HAVE ALREADY RULED OUT

– Co-channel interference: the nearby AP was moved to a different channel.
Retries improved from 63% to 49%, but the disconnections continued unchanged.
– Solenoid / valve current: 0 of the 37 disconnects occurred while a station
was running (watering accounts for 3.8% of the time, so chance alone would
predict more).
– Controller reboots: only one power_on reboot in the whole period; the
disconnects are not accompanied by restarts.
– Access point moves or reconfiguration: the AP layout was unchanged for two
days before the update, with zero disconnects during that time.

QUESTIONS

1. Is a WiFi regression known in 2.2.1(5)? I noticed the release notes mention
updates to the OpenThings Framework and TinyWebsockets libraries.
2. Could the new build have changed how the ESP8266 scans or selects an access
point, or how it behaves with 802.11ax/be beacons? The AP it refuses is the
only one here advertising WiFi 6/7.
3. Is os_221_rev4.bin available anywhere? https://raysfiles.com/os_compiled_firmware/v3.x/
only hosts os_221_rev5.bin, so I cannot roll back to test whether the
previous build works.

Controller: OpenSprinkler v3.x, firmware 2.2.1(5), hardware unchanged.
I am happy to run any diagnostics or provide logs.

Thank you