I had a problem with SU-8 on glass slides that I thought was poor adhesion
but it turned out that I was just exposing it for too short a time.  Any
company that makes photoresist will be quoting the doses as they should be
on Si which has a reflective surface.  This causes the light to be
reflected back across the photoresist essentially doubling the dose that
you put in.  When working with glass you don't get this reflection of your
dose and you need to double the original dose you put in.

Bottom line, try exposing it for double the time that you expect.

Nicolas Duarte