I had a feeling you used a food processor. I'll bet you don't do THAT again. Too much mixing too fast (like a blender or food processor) does something to the starch and turns it to "glue".
And think....... it's easier to clean a couple beaters than a food processor! ;-)
Sheesh
They came out terribly!
All is not lost however..
I have a few spots of wallpaper that have come loose!
Ms.B
It's also possible your taters were a little old? As potatoes age the starch turns to sugar and that can make them gooey when mashed!