We found a bug in the weather script a couple days ago that may be related:
Specifically, I noticed that the ‘precipitation_today’ data returned from WUnderground tends to be empty (instead of 0). That was causing the script to throw a NaN (not a number) value, and later causing the calculated watering percentage to fall back to 100% due to not a number issue. This probably explained why there were lots of ‘stuck at 100%’ problems. I wish they put a filler 0 as opposed to returning an empty string. But the bug has now been fixed and deployed.