We just successfully migrated a SSRS 2016 instance to PBIRS. Users are reporting weird behavior when trying to enter data in a multi value parameter.
When they click on a parameter to enter in data, normally a drop down text entry appears and they type in multiple values. That still happens, but the box goes renders to the bottom right of the screen and you only see that box on the screen (see picture) This happens in all web browsers.
EDIT: It appears that the box is showing where the parameter is supposed to show up if the report is full screen. I cannot see all of the parameters like we used to in SSRS