I have recorded 9017 attempts (and counting) across about 45 different Dark/Light/Cantina/Fleet nodes with 3065 total drops giving me a 34.0% overall drop rate. Having said that, I've had multiple streaks where I've had low drops. It all comes down to the probabilistic nature of RNG. For a truly random set of events, it's easy to calculate what the likelihood of having a bad streak is using binomial distribution functions. Getting 20-25% drops over 150 attempts is definitely on the low side, but there is still a 0.2% probability of that happening in any given sample that you come across. In other words, the odds of that happening are low (500 to 1), but not negligible when you are doing this many times.
From my statistics, individual nodes have varied from 26.9% up to 43.8%, but the statistical probabilities of these outcomes for given sample sizes are only below 2% for a couple of outliers. At one point, I had an extremely bad run on Xanadu Blood (35 of 162 or 21.6% ), but it has since popped back up to 27.1% .
Last thing: RNGs are never truly random. They are generated by one of various computer algorithms, all of which have some bias. However, the typical RNG biases are so low, that you might only barely notice it in samples numbering in the trillions.