I would suspect you've got a Presta valve stem passing through a Schrader-sized hole in the rim.
The Presta hole should be 6.5mm across, and the Schrader is 8.5mm That's not a lot of difference, but its enough for the air pressure in the tube to push the valve out the rim-hole a little, where it is cut or sheared off.
Measure the holes first to be sure, compare your front and rear wheels too.
You have three options:
Buy a schrader-valve tube or two.
Buy/make a spacer/bushing
As a temporary hack, you can wind one of the retaining nuts onto the valve stem before installing into rim, and a second nut can go on afterward. Avoid overtightening either nut - fingertight is fine.
Then inflate tube like normal - probably 40-60 PSI for a MTB tyre on the road, and less for offroad usage.
Update - searching your bike brand returns
Rim - Bontrager Connection, double-wall, 32-hole, 20 mm width, Schrader valve
This reinforces the "wrong valve size" idea.