Hi ,
variables are created on info-object level but not on multi provider/infoset.
ex: take the standard variable 0s_plant , it will available in any targets where ever matplant is used, same applies to custom variables as well.
hope you are saving variables after creating them along with query?
create a new test query on top of infoset/multiprovider , and see if you can see all variables under matplant? or not?