First, no the app didn’t break support with previous firmware versions. To double check, I loaded 2.1.3 and tested, no issues.
To troubleshoot, does the IP on the OpenSprinkler (press B1) match the IP in the app? If not, maybe you have DHCP and the IP changed. If this is the case, you should setup static DHCP reservation in your router to prevent this.
Otherwise, try opening the IP in a browser see if the UI loads that way and let us know.