When I try to use scrollX together with chosen (1.8.7, the last version released in 2019) and scrollX, sideways scrolling works fine and even the headers scroll horizontally, but the chosen dropdown contents disappear under the table.
Oh... I forgot to mention that eonasdan-bootstrap-datetimepicker dropdowns also disappear under the table data, so I'm not sure chosen is relevant here at all.
When I try to use scrollX together with chosen (1.8.7, the last version released in 2019) and scrollX, sideways scrolling works fine and even the headers scroll horizontally, but the chosen dropdown contents disappear under the table.
This only happens with multiselects.
See:
http://jsfiddle.net/delgado/w6uveydq/21/
(Forked from a previous fiddle but I made sure to remove all irrelevant bits.)
(Sideways scrolling will be possible if you make the rendered output smaller and to see the problem you have to click on the "position" dropdown.)