It's not an issue - its just RNG. Just be prepared to spend a lot of vials and protections - like many have said in the past. If might have to spend to get frags just for the skillbooks if you want to max the upgrade you want (for kakuzu: passive 1 is the one you should focus)

There's a recommended order to focus in getting skill breaks: https://forum-narutoen.oasgames.com/page/show-post-42049-1.html. I would put mystery as 3rd instead in my opinion.

Every ninja that has skill books have different orders based on what they have but kakuzu, the passives are the most important. Order is suggested due to the lack of how easy protection vials can be given for free. So you want to make use of every little protection vials you have.