Was just looking at my logs and I am seeing the same error. It's occurring in two rules , both with a similar triger as OPs. In my case it's humidity sensor increase.
Errors:
app:7582023-10-17 12:32:08.660errorinvalid operand type for 20.95(number) decreased 20(number)
app:7582023-10-17 12:32:08.655errorinvalid operand type for 20.95(number) decreased 20(number)
app:7512023-10-17 12:11:43.304errorinvalid operand type for 20.56(number) decreased 20(number)
Just realized I am still getting this error as well. For me it is a Humidity increase. Just noticed mine is a bit different. As the final part in () says string? not number.