Aside to the main point of the thread, but I’d be very surprised if the Fallen London RNG was anything other than industry standard (which probably means supplied by an AWS machine that’s also feeding numbers to a thousand other applications including online banking).
The chances of failing an 82% check five times in a row are very low - about one in fifty thousand - but it will happen occasionally. Enough people have been playing FL long enough that one in fifty thousand chances will have happened to quite a few people. In fact, given that each player gets (in theory, assuming they never sleep) 624364= 52,416 actions per year, the statistical expectation is that everyone who’s been playing for more than a year or two will experience one.