Having similar issues won't power up but with cover off and a magnet held near the power switch it will and runs fine. When I put the cover back on most times won't power up until I found a powerful magnet that held outside the cover where the internal magnet is located it comes to life ?
Magnet lost its strength or the Hall effect /reed switch is not sensitive enough ?
I thought about glueing a neodymium magnet to the inside of the case but not a lot of space when put on.