K4 pedal soft?

Not super soft but easy to depress whereas other times the brake pedal is more firm and I have to apply more pressure

So far this week it was normal no firm pedal it easily depresses and starts up fine. Just noticed on occasion when I press the brake prior to starting it's more firm while other times it is more soft not spongy just softer.

Also wanted to clarify that this doesn't happen when I'm driving the brake only has intermittent stiffness right before I start the car and then depresses once ignition turns over.

Ok so my main question is why the intermittence? Is it based on like driving habits or humidity or something like that that would sometimes make it more firm and other times more soft? Because if I pump the brake while the cars off I noticed the stiffer the brake gets but usually when I drive I just put the car in park and don't push on the brake while it's off then a few days later I go to start car and the brake is stiff

Does this happen intermittently? Is that a normal function or is that indicative of a leak somewhere? Because there's times where it's stiff 2 days in a row when I start the car while others the brake is a lot softer and easier to depress for days at a time then suddenly stiff again, even if car is sitting over the weekend untouched

Are those commonly problematic? My grandma has same car no issue

My grandma had a similar situation where her brake pedal was super stiff and took a lot of force to depress but she had auto hold mode left on, would that have caused it? Because since then she had no issues and she had a multipoint inspection at the dealer after that incident

I know when my grandma had that issue they did a diagnostic test and no codes so she should be good right? Would codes come up for that type of issue

I don't have a scanner. Question when I first got my car it was inspected prior to selling shouldn't they have caught that if there truly was a vacuum leak?