Random reboots have a lot of possible causes and you can find lots of solutions and tips here.
Could you describe your issue a bit further? When and how often does it happen? Can it be reproduced or does it happen randomly?
If you are sure it has to do with the update than the first thing to try is to reinsall the update instead of downgrading. Sometimes something goes wrong during updating and issues occur, but that doesn't mean it's the update's fault.