if I am wrong others may correct me
but I think there was also a french standard
of 22.0 mm or something quill diameter
if you try to use a 21.1 stem in a 22.0 steerer
I bet it wont work too well

otherwise
steerer tubes are often internally butted
and if the stem is inserted too far
the butting interferes with the stems ability to hold itself in place
so make sure this is not the case
simply by raising the stem close to its min insertion mark
and seeing if it can be adequately tightened