Is what you’re experiencing now new behaviour since updating to 2.1.0?
Reading your posts, it looks like your reset the OpenSprinkler a few times with no effect. Then you reset the OpenSprinkler and the WiFi bridge and then you could access the page. Are you sure that the issue is not the WiFi bridge? Can you report the RSSI for the bridge on your AP and the bridge? You can test this by resetting only the WiFi bridge the next time it happens.
Also, are you running the UI from the SD card?
There was an issue with the upstream ethernet library, but it’s not often triggered. When the problem is triggered it results in a soft-lockup and the OpenSprinkler is rebooted by the watchdog 2 minutes later. The upstream fix has been incorporated into the 2.1.1 firmware.