Unable to get a tube replacement to last
There is a mark in the middle of the valve stem as if something has pressed against it:

Given that it was a fresh new tube, it likely means that it had been installed with the valve protruding at a sharp angle from the rim hole. Externally, it will look like this:

This is bad because the air pressure creates additional uneven stress to the rubber around the valve. Which, in turn, may cause a blowout at the end of the metal tube of the valve, or even tear the whole piece apart.
At the installation time, while the air pressure is not too high (but not zero), pull the valve up with hand to ensure that it sits at an angle as straight as possible to the rim surface. If it is already stuck, deflate the tire again and repeat the attempt.
While you are dealing with the problem and have your rim exposed for inspection, check that the valve hole is smooth on its edges both inside and outside:

Any sharp burrs left in it will rub against the valve, which will also weaken it and will create a possibility for a blowout.