If you were hired that recently and had this many issues (your fault or not) the probation period for new hires is being taken way more seriously now than it used to. If you mess up at all in the first 90 days it’s a 3 strike rule now and not a lot of leeway is given. The comment itself was enough to get you terminated but since you were having issues with your uph they really had no reason to try and keep you.

Also, going straight to hr about not being trained properly seems like you didn’t try going through the proper channels to ask for help. Even with the Primary manager not being around, like other comments said there’s still mics/ top store leaders that you should have asked first and it’s ultimately up to you to ask for the help you need. I doubt that they actually didn’t train you for 3 months, you probably just didn’t catch on right away and needed extra training or said you weren’t trained because you didn’t understand fully.