Body battery not Measuring on Lily 2 Classic

I've always had issues with body battery since getting this watch, but I usually wear my Vivoactive 4S at home, changing to the Lily 2 Classic for work day.

The Vivoactive will give a body battery in the morning, and then do some catch-up magic at night, but during the day the Lily 2 isn't measuring my body battery at all.

I wore the Lily to bed last night, and it recorded my sleep and gave me a sleep score, but then when I check the body battery it tells me I didn't wear my watch to bed.

Has anyone got a fix for the body battery issue? I know it was a problem on the original Lily, but not sure if it's just my watch this time??