Add a little fresh discharge base (clear discharge) to the batch to lower the viscosity.
Also maybe try it in another screen to see if the screen could be the cuplrit, and not the ink itself.
Also could just add a little water as well but clear discharge base would likely not lower the performance as much as water.
I don't like how white discharge performs anymore, I just do white HSA now 3 screens to make it bling, yes it has hand, but it looks great.
Eric knows more than me though so maybe he'd say the above is bad ideas, I know Matsui used to have a thinner which was basically water with specific PH for refreshing water base inks, maybe Magna has something like that, but I'd first try a different screen, then discharge base, then water and see where that gets you for a quick fix.