Backtesting End Date confusion

Not the most important issue but its a little bit annoying….

I have multiple instances of a bot,  with different settings on US30 30m.

They are currently all stopped and I am doing some backtesting.

For back testing they all have the same start date but when I try to select the end date, for some the last date I can select is 31/12/2023 but others the last date is 19/12/2023. 

For the ones with 19/12/2023 even manually typing in 31/12/2023 just turns red and on tabbing out it resets back to 19/12/2023

I even have 2 instances with exactly the same setting where one can select 31/12/2023 and the other 19/12/2023

Why?

and how do I fix this.

Tks

Rob