Hello and sorry for the late reply due to xmas vacation.
I have just tried the exacty Unity and Slate version you provided and there was no similar problem at all.
Hmm. Does this also happens for you after restarting the Unity Editor?
When error occur, I need to re-create again my whole project to solved the problem.
But, what’s a caused? I’m very confuse.
Problem occurs accidentally after I add other unity plugin gradually.
Some time okay, some time K.O … depend on luck.
(Very troubled)
Maybe, slate conflict with other unity plugin or I don’t know.
I need a test to defined it.
I will keep update when I doing further.