Hi,
This is my first post, so I hope that it is relevant.
I am using Time Machine in engineer mode with view user variables open in order to to monitor values.
The selection variables back_price/2/3 appear to no longer be returning any values.
This also appears to affect other connected variables such as back_amount, etc.
Looks like you are on to the root cause, but just in case, I am not a window cleaner, so no ladders involved!
Can I add that I have had great support form the Team.