Brush tool not working when using layer mask

[Saabirah37757134rx1e]

Hello, I am having a problem using the brush tool when masking. I am doing an assignment for school following Youtuber, PiXimperfect's tutorial on how to 'Check & Match colors Precisely in Photoshop'. My brush tool worked fine on previous layers until doing a 4th Curves adjustment layer where my brush - a soft round one with 100% opacity level and flow level set to 6% for the sake of the tutorial- started to act funny.

This is before I use the brush on the Curves layer:

Here's how the brush tool acts when trying when using it on an inverted black Curves Layer:

I'm still very new to the software and I'm using Photoshop 2024 CC on a Windows 11 OS version 23H2 laptop. Thanks to whoever helps.

[c.pfaffenbichler]

Could you also include the Brush Settings Panel in screenshots? 

Is any Selection active (try Select > Deselect)? 

You seem to have painted something, the thumbnail is different in the two screenshots. 

[Saabirah37757134rx1e · Accepted solution]

Hi C.pfaffenbichler, I just found the solution thanks to these previous posts: https://community.adobe.com/t5/photoshop-ecosystem-discussions/brush-problem-is-showing-gray-square-... 

https://community.adobe.com/t5/photoshop-ecosystem-discussions/lagging-square-areas-appearing-while-... 

And so far, the software is working fine again. But, thank you for your attempt to help.