My guess is either FoD (it does happen to the best looked after aeroplanes), or ice - it's that time of year and it sometimes forms in strange places and strange ways - even if you think it was warming up. If nothing is found and the aeroplane is fine next time - it was probably the latter. Unnerving of-course, because you can never be absolutely sure!
Should you ever meet this in the air (deities forbid) it is actually reasonably easy to fly most light aircraft with any single primary control lost (although it can be much nastier if it fails offset, or close to the ground where you've very little time to adapt). As a general rule...
Failed ailerons - use the rudder
Failed rudder - just don't use it
Failed elevator - use the pitch trimmer.
The aeroplane should then be flyable, badly uncomfortably and inelegantly - using the controls very gingerly, avoiding anything more than 15° of bank, using a very wide circuit, to a messy but totally survivable landing.
Anyhow, this is pure conjecture and rambling on my part. Let us know what gets found out - there's almost certainly a sage lesson in this for all of us. (In fact there's already been one- to do with pre-take-off checks!).
G