It also could be as simple as not tightening the coil into the base completely.
There's no need for subtlety here, crank the coil into the base until it bottoms.
Use a towel to give a better grip if you need to.
That's the coil into the base. The base into the tank should be tight but it's more obvious when it's tight enough.
That little post ain't much to grip on and it could be an issue.
A different issue that relates to tightening things:
Don't crank your
tanks down into your battery till they bottom.
Different tanks have different length posts.
The longer ones can push the contact down into the battery and wreck it.
It can be pried up with a pin if that happens but my first $34 VV 1200mah Mega V2 ego was never the same.
Tanks only need to make contact. You'll find the feel with time.
Nobody told me cranking it down could wreck it. It did. It was an expensive lesson.