Remove it again fully, catching any water that should come out.
Fully clean the filter unit and its seal/s, also the housing it fits into making sure there are no foreign bodies that would impede the sealing faces.
Might be an idea to pop a make and model up incase you need a spare 😉
If its been in storage that length of time , the rubber seal of filter may have perished slightly.
try lubricating the ruber with a small amount of olive oil. The same thing sometimes happens on Caravan water filters & toilet rubbers when they are not in use for extended times.