Endurance Score dramatic drop

I finished an indoor workout last week and immediately my watch displayed my 'Endurance score' dropped over 200 points.  This is the 2nd time in just about a year this has happened.  My training has remained steady while also following a Garmin Coach workout plan.  

I am enrolled in the BETA program and am not sure if this is happening following a software update or if that would have any correlation to the dramatic drop.  

I have tried to chat with customer service and sent them pictures of the dramatic drop but have not had any success as they tell me they have no clue what is causing the issue.  

Any one else having this issue or might be able to suggest something to help?

Attached is the photo from my watch showing the drop.