In my case I've been storing since my teenage years in my mind a lot of "points" I couldn't agree with or for which I couldn't find an explanation. I just tried to keep them concealed hoping that as an adult I would change my mind on some things or that I would come across some sort of information that would make things make more sense.
I think that the first points were preaching (I hated it, it was an eternal frustration) and secular chronology vs Bible (like Egypt being out there as soon as 3500 BC).
Then I started feeling uncomfortable with the shunning issue, the relationship with non-JWs and the way JWs are allowed to "confront" ideas (yours is the truth, don't let anybody change your mind, invite others to our meetings but don't go to theirs...), and of course how university is frowned upon.
After that I remember being against encouraging children to get baptized, how most JWs are so judgemental when it comes to music (I started listening to heavy metal).
And as part of my training as a teacher, you have to study how education changes people's lives and makes societies prosper, and you are presented a lot of info about the improvings that have been achieved in poor countries and how poverty is being reduced. That was much different from what you hear from the WT, so maybe "the last days", are not such a thing... Apart from the fact that you know that earthquakes are a natural phenomenon.
I could go on with many other aspects and this process is not linear, I had moments of "spiritual recovery". However, I remember one night in 2014 when I realized that if I wanted to be an adult, or a whole and coherent person, I HAD to leave the JWs. After that moment I destroyed my investigation boundaries and read about Evolution, Crisis of Conscience, info about 607, the Australian Royal Comission, failed WT and Bible prophecies...
And that sums up my whole process. Now I'm on my way to complete my exit from the WT.
I hope you find this information interesting and/or useful.