My two cents : I don't agree with your first premise:

> The transition from a PhD position to a postdoctoral position: A postdoc has to work much more independently than a PhD student, and maybe people struggle with this.

My experience of supervision as a PhD student :
- First 2 month : 30min / 1h talk with supervisor ~ once every two days during lunch.
- Following 6 months : The same, once a week
- The second year : A 2 hour talk, circa every month
- The 3rd year: My supervisor left and was replaced with another one. A 1h talk circa every two weeks or so.

I would call this very independant work, as I was basically making all the calls, I just needed to justify them adequately with my supervisors. I did not go for a postdoc afterwards (I transitioned to industry), but I doubt a postdoc position would have left me "less independant".