Very strange behaviour in brushing a mask

Hi guys, latest PS beta here (25.0.0). If I brush a mask with a solid 100% flow and opacity standard brush, I can still see a very little part of the part brushed, like 5% opacity (and brushing more on the same area doesn't do anything). I've tried everything, reinstall, import default brushes, nothing, there is no way to brush a mask at 100%. Same file opened in PS 2023, with same brush option, everything is fine. BUT, if I turn on the mask channel visibility in PS Beta (standard red colour), something is happening. If I turn on the alpha channel after brushing, and I brush over I've already brushed, the red from the brush is darker and the area is brushed 100%. If I turn the mask channel visibility on BEFORE start brushing, the brush is 100% red and everything is as it is supposed to be (but it's difficult to work like that because you can't see in real time what you're doing). The issue is real and is reproducible. Attached examples

Original image. Duplicate the background.Clean the background

Here is brushing with 100% brush, no way to eliminate it at all

After turn on layer mask visibility, you can spot that in the middle the red is not as darker as the surroundings. If I brush over, I can make the red the same, and the visibility is 0%

here is a brushing if I turn on layer visibility before start brushing: solid red and 100% brush (0% visibility)

now is gone, 100% brush and 0% visibility

[Mod: Moved to the Photoshop Beta forum]