Besides for seed choice, your issue might lies in the choice of the Pseudo-random Number Generator (PRNG) that your R environment is using.
R usually implements the Mersenne Twister by default for generating random numbers which are then scaled to a range between 0 and 1 - thus simulating uniform random variables. The other distributions can then be simulated via the inverse probability transform.
For a easier understanding of how PRNGs work- check out this Kahn Academy video.
Additionally you can also check out the R documentation on this topic:
If you want to look at implementing different PRNGs to see what happens "under the hood" with R. I am in the process of developing an R package that allows users to implement different PRNGs via functions. Check it out here.