So was I, but I still had problems. Redoing the connection eventually solved them. I think it’s very fussy, as any voltage drop, even small may confuse the protection circuit.
I’m assuming you’re using a new battery? When you receive a li-ion cell, it should always be charged at around 40% capacity. Note as well it has to be an unprotected cell, most 18650 cells are sold with an IC built in.
The second time I did this replacement it was more troublesome than the first, I had to redo it twice and it then took a few charging cycles to behave reliably for some reason. But eventually it gave me the normal 5–6 hours of use. Good luck, it takes a bit of patience.