Lately I've been getting splits at the bottom of the tubes value…is there a reason why this is happening ? Thx

Valve?

Check rim tape and sharpe edges, try diffrent make tubes and be careful when you install.

cheap innertubes or presta valves in shraeder drilled rims.

Tyre could be moving on the rim and taking the tube with it. You could try some talc on the tube or a couple of drops of superglue on the tyre bead on one side. It used to happen a lot to my group with old skinwall tyres.

Try some talc, then if the tyre moves it won't take the tube with it.

APF

Cut a square inch of old inner tube, poke a hole in it and use it between the tube and the valve hole.