Photo Stream missing pictures

Hello,

Here is my question..

I have an iPhone 8 and I use it to take photos all the time. To transfer my photos to my laptop I use "my photo stream" but I don´t use iCloud to storage my files.

Whenever I take a photo on my phone I can see how the photo stays in the camera roll and then it automatically goes to the photo stream album.

The problem is that sometimes some pictures don´t get transferred to the photo stream album and I don´t understand why.