Chosen Solution
Miele Compact C2 Electro + Powerline. I suspect it’s the electrical connection because the power to the beater head turns off and back on pretty randomly during use. It used to seem like various maneuvers like shaking it would bring it back on. Fixable? How? Thank you!
Your carbon brushes in the beater head are likely worn down. You can fix it! Try giving the side of the beater head a good whack and see if that settles things into place. If not, time to do a disassembly.