What is that hashed out area?
Factabulous wrote a decent post looking into the hatching here:
https://forums.frontier.co.uk/threads/facts-new-theory-of-hatching.477450/
If I had to summarise that whole thread in my own words, the hatching acts a little like an S-R latch, but things get weird around the None state.
EDIT: S-R Latch in a nutshell... lets say you have a light which turns on when a certain level of darkness is reached, and turns off when it's light again... let's say that level is 0.5, where 0 is total darkness and 1 is daylight.
Because light levels are one of those things that can vary, your light might start flickering on and off because the light itself sends the light levels 0.5 again, then below when it turns off. An S-R Latch sets a different upper bound for the light to switch off again. So your initial state might be light is off at 0.6, and turns on when it drops below 0.5. But it won't turn off again until the light level reaches 0.7. Conversely, it won't turn on again til it drops below 0.5. It stops rapid switching between the two states.
The hatching represents that little bit between 0.5 and 0.7.