Just got a very interesting issue, in Bootstrap open modal A and B in order, then close B keep A open, you will find scroll is not working for A, after check it's a problem of Css, the solution is

{ Solution }

.modal { overflow: auto !important; }

add this css rule to the scope that you want it working, biu problem solved!!

{ ref. }

https://stackoverflow.com/questions/36460538/scrolling-issues-with-multiple-bootstrap-modals