I consider most problems over the vaccines are because there is really no history for them so they really don't know a pile of things. Those are things like really not knowing how long a vaccination lasts. The other thing is Covid itself which they are also learning new stuff, seemingly every day.
The problem, I think, is that there are those who expect the medical/science community to have all the answers and they don't. So, every now and then, they change their suggestions and this makes everybody very upset. I also believe there are a LOT of people working, very hard, to learn all they can, as fast as they can, and should not be blamed every time they learn a new thing and pass it on.
I always find it interesting that those who get upset when something new comes up, and instructions change a bit, expect perfection but tend, I think, not to be all that perfect themselves.