On OS 3.2, the Ethernet adapter works as follows: if it detects the adapter, and it can successfully obtain an IP address with the adapter, it starts in Ethernet mode; otherwise it boots into WiFi mode.
To find out why it doesn’t go into Ethernet mode, first check if (upon power on) does it show a ‘Start wired link’ message? If so, that means it has detected the Ethernet adapter, and if consequently it quits Ethernet and boots into WiFi, then it must be because it can’t obtain an IP address. I don’t know the specific reason, but it could be because there is something wrong with the static IP settings (for example, IP conflict, incorrect gateway IP setting etc). Generally I recommend users to stay away from setting static IP, and instead use their router’s DHCP reservation to reserve a fixed IP. This way, the controller still gets a fixed IP but everything is managed through DHCP.
Finally, if you purchased the controller from our German distributor, they had a first batch of OS 3.2 with a slightly outdated firmware, which may have affected static IP. The most recent firmware is 2.1.8(4) (i.e. minor revision 4), and is available here:
https://github.com/OpenSprinkler/OpenSprinkler-Compiled-Firmware/tree/master/v3.0
you can perform a OTA update (note that OTA update only works in WiFi mode, either AP or station mode is fine) to update your firmware to the latest. But I would say first try to set the controller back to DHCP, and use your router’s DHCP reservation to bind a fixed IP to the controller’s MAC address. If that resolves your issue, there is no need to update firmware.