I had the same problem recently with an old v2.3 unit. I changed some network config at home and rebooted the OpenSprinkler from the app. After this the screen remained blank (but with the backlight working).
„Resetting“ the Unit from the App or webpage didn’t work and I almost gave up before googling a factory reset. So I exported the config and did a factory reset. During this the screen operated as normal and after the reset everything worked fine. I then restored the config and, amazingly, the screen went blank again.
So the problem was with the config. Another factory reset and manually set up the unit again and all is fine weeks later. So the problem was a corrupted config.
I also suffered for a long time with wrong date / time being displayed (others have complained about this too). I always had an entry in the NTP IP address setting as I thought this was needed. After reading another post recently I deleted this to use the default NTP Servers. Wow, the Unit now always shows the correct date and time…
Hope these ramblings help!