Using (or at the least trying to use) the 2019 software. I noticed a mistake in a frame of an animation loop I'm doing and went to erase it. I went into the symbol, into the layer where the mistake was, and tried to erase it. Nothing happened. I figured I could deal with one thing being on the fritz and that it would probably resolve itself. I decided to try selecting a color I had on another layer to draw over the mistake, so I went to that layer and tried using the eyedropper tool. That didn't work either. At this point I was getting frustrated, but I knew I could still select the color I wanted to use in the properties of the brush and draw over it the mistake that way. That didn't work either. For some reason, the brush tool is either set to some void of color (dark grey with grid lines) that erases things I've already done when I try to draw, or it draws things invisibly and I'll need to click on the frame I've tried to draw on to even see that such a thing happened. I've tried looking for answers on previously asked questions and couldn't find any that would help. I've tried closing and reopening the file. I've tried rebooting my computer. Nothing is working. Please help me.
I'm afraid this isn't the most helpful answer, but I've had similar experiences to what I think you are describing when working on animation projects that have gotten very dense, with a lot of nested symbols and vector art. The only solution I've found is to copy all of my layers and paste them onto the main timeline, make my edits, and then copy and paste them back into my symbol. For some reason it seems like animate has trouble with the drawing tools workign incorrectly inside a symbol when projects get too resource intensive.