The issue is that the header container must have overflow: hidden - otherwise the parts that are out of scroll view would be visible! But the Bootstrap select there is being placed inside that container - thus it also gets cut off.
What you need is for the dropdown to be attached to the body and then use CSS positioning to put it in the correct location in the document. I've just had a look at the Bootstrap Multiselect options but there doesn't appear to be an option for that. You could perhaps ask in their support channels.
There is no other workaround for this that I'm aware of.
Hello,
As you can read here : https://datatables.net/forums/discussion/comment/216696 there is a conflict between multiselect used in a Datatables with fixedColumns Creator have the following answer :
You can find a test case here : https://jsbin.com/hitucal/edit?html,js,output
Have you got a solution/workaround ? Thanks