Has anyone had problems with the brake pedal going hard when slowing down

Does it feel like it's vibrating and pushing back against you?

If so that's just the ABS kicking in. Edit: It can be very unnerving if you've not experienced it before.

If it's doing it when it clearly shouldn't be (i.e. you're not driving on slippery conditions) then it'll need looking at.

Best get it looked at.

why does my left hand front wheel lock and skid when l brake at low speeds(10-12mph)

You could be suffering from 'brake grab'. Google for that and you'll find there are a number of different causes like binding pistons, pad contamination from brake fluid leaks etc.