BK WF feature "add" look like not workfing anymore

Hi
I am on a dedicated servor and we are experiencing a very weird issue.
We have BK WF that use the “add” opérator to a list field.
Looks like it does not “add” anymore when there more than one value in the fiels
We use this BK WF for 1 year and it never bug like this before
Any idea ?
I filled a bug report

Lists are limited to 10k itens and you can’t insert an element that already is in the list.
Is this the issue?

I don’t know if what you are looking for is a way to add, at once, multiple items to an existing list.

If so, what you can do is use the command :merge

List1 SET LIST List1:merge List2

No I only few items
Thanks for the comand, I ll try this one !