Basically, I do not know. Davies Media videos come under the life-is too-short category 
You could add a screenshot showing all the layers and layer-masks you have.
As a guess, are any of the layers marked with a layer-effect icon (fx) ? This can affect some procedures. Click on the (fx) in the layers dock and merge the layer-effect (s) That gets you back to a Gimp 2.10 state.
You could add a screenshot showing all the layers and layer-masks you have.
As a guess, are any of the layers marked with a layer-effect icon (fx) ? This can affect some procedures. Click on the (fx) in the layers dock and merge the layer-effect (s) That gets you back to a Gimp 2.10 state.