Related to animation, ive tried to copy and paste a frame to duplicate it and right after that any of the brushes wont work, it is drawing but its not - the file size is increasing but there are no visible changes, i use a mouse only, please help!

Which version of krita are you using and which operating system?
Can you post a link to a full screenshot (.png) showing your layers docker, timeline docker and animation docker?
How exactly did you do the copy/paste action on the frame?
Did the frame get duplicated properly?