The general lesson here is that, even for a high quality PRNG, you can’t assume a random distribution unless the generator’s cycle length is much larger than the number of random values you’re generating. A good general heuristic is —
If you need to use n random values you need a PRNG with a cycle length of at least n².
From a 2015 post by Mike Malone on PRNGs vs. random key collisions. The Chrome/V8 bug that caused Mike to write nearly 5000 words to explain has since been fixed, but you can check your browser’s PRNG here.