Brush tool in layer mask not working all the time

[Riqs]

Hi there

I am a new user with inconsistent use of Affinity,

That being said i have watched the tutorials and just reset my desktop version and managed to get the brush tool in masks to work  using black and white to reveal and hide  layers.

The problem is it sometimes works and then doesn’t. I do the exact same thing and the brush

wants to cut out the image rather than be a brush . Any ideas on what i am doing wrong?

I have tried using the brush from the layers panel 

and again sometimes it works and then it doesn’t,

Macbook  2014 Catalina 10.15.6 Sony Raw images

Thanks for any help / insight 

Rick

[stokerg]

17 hours ago, Riqs said:

I do the exact same thing and the brush wants to cut out the image rather than be a brush

Do you mean it makes a selection, like marching ants?  If so, then you've likely got the Smart Selection Brush selected and not the Paintbrush Tool.  But if that isn't it, if you can post a screen recording, that will be a big help  You can easily record your screen by seeing this link