A few days passed, and I was finally able to measure all cells. I was quite surprised that the whole capacity of the scooter went to hell because of one cell. So far it looks like it. You can take a look at the table. 2800mAh is basically full capacity. These batteries are usually rated somewhere around 2800 - 3100 mAh. Looks like I need to replace only one cell and I can reuse the rest. This is my plan for now. In the next step, I will charge every cell to the same voltage it had before.
Next time we should start building the battery blocks back again.