I don’t know if this applies to your situation. This morning I notice that I was not watering. I has not rained in a few and their is a heat advisory. A quick look at the iPhone app revealed that watering % had inexplicably changed to 0 %. I changed it to 100% and got on with my life. Could perhaps, when watering is suppressed as it was Monday, the watering % is ‘sticking’ at zero?
If this is the case. Then my observation might fit with yours.
I am running 2.1.6 without other issues.