Hi @pavel.junek ,
Please have a look at the eazyBI community post discussing a pretty similar question - How to list all assignees of an issue in particular status.
The suggested formulas focus on the changes during the status. If you want to include the assignee in the case it stayed unchanged during the particular status, you can add another condition inside the Filter() function:
...
OR
([Measures].[Issues history],
[Transition Status].[In Progress])>=0
...
The report then could look similar to the one below:
Best,
Roberts // support@eazybi.com