Just a couple of guesses.
In no particular order.
Bad coil head.
Coil head has become loose when you opened to fill.
Bad connection between 16b and MVP
Problem with MVP
Try swapping your 16b with another clearomizer or topper to see if you get a different response from you MVP.
Or dance naked around the device with a rose in your teeth while patting your head and rubbing your tummy to see if that helps.
Probably not but it will give you a reason to do it