"Sticky" Multiple select for Users

We are experiencing large in- and outflows of our colleagues which are spread out over the year.
When offboarding, the admins then deactiviate or inarchive the users in WebManuals.
After having contact with WM, no possibilities appears to be in place to import files to deactivate all the users in bulk.
Therefore, all users must be deactivated manually.
The column for users does have the feature for multiple selection. However, this multiple select only works when selecting users in 1 go. It does not work when you select one user, then search for the name of another to select it. 
Scrolling through all users would be unlikely, as we have over 10.000 users. 

Our wish: a multiple select feature that remembers the selected users, when using the search bar as well as scrolling through the user list