Brush tool not working when using layer mask
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.
