Ignition will randomly lock sometimes, and key wont turn.

Definitely annoying scenario,

Prior to turning the key when the steering wheel lock has been engaged you may need to apply turning pressure on the steering wheel itself. The steering wheel lock pin is a pencil-sized pin about 1/2 inch long or less. Overtime it begins to get grooves in the smooth sides of the cylinder pin. Turning the steering wheel to the left and right while turning the key at the same time will unlock it most of the time. Permanent fixes will be to get the pin replaced and or the worn out key or key lock cylinder

The problem most likely is the cylinder lock cable that goes from Gear shift selector (P / N/ R / D / OD) to ignition switch. If you take off center console to allow access to shift selector there is a screw on the left hand side of selector main body that attaches to cable. The cable is self adjusting according to service manual but I had similar problem. I loosened screw and shifted the selector from P to N and back to P then retightened screw. Not sure if this would be directly linked to servicing the alternator but who knows what the mechanic did in their process of fixing the alternator. Good mechanic will at least do some steps to ensure that is indeed the problem with the vehicle and not waste your money or time. Im assuming the vehicle wouldn’t start if the alternator was bad and left the battery discharged. So any mechanic is going to test starter, ignition switch, ASD relay, Alternator, and so on. To test ignition switch he might have unplugged the cylinder lock cable from ignition switch. i hope this helps.