From what I've read, the Seychelles problem is that they were all given one of the Chinese vaccines, and there are considerable doubts about its efficacy. So even though they were heavily "vaccinated", the vaccine isn't very good. Lots of breakthrough cases.
In Israel, it seems to mostly be the unvaccinated folks: children, people who refused to get the shots, people who only have gotten one shot. But there are some people who are fully vaccinated who are coming up positive as well. What the article said is that the Pfizer vaccine, which was like 95 % effective against the original strains, is only around 85 % effective against the Delta variant, so there are going to be more vaccinated people who may come down with it as well.
If you are fully vaccinated, but fall into one of the high-risk groups, you might want to be very careful.