Weird rumble scores
2 would explain a bit of a score decrease, although not that many bots save data. I don't think 1 is true; sure some 100%s will become 99.5%s but also some 99%s will move up to 99.5%. Without 2, the APS estimated from a small number of battles should be an unbiased estimate of the true APS. And it takes 1 APS decrease in 100 bots to get -0.1 APS since there are ~1000 bots in the rumble!
Have a look at 0.14 and 0.14a, the APS is 0.3 diff. And if only looking at the simplest bots to beat, 0.14a is having more 100% than 0.14, simply because it haven’t got enough battles.
99% going to 99.5% does happen, but they do move to 98.5% as well. It’s mostly balanced.
But the 100% part is onesided, causing it to constantly move down before reaching some “stable point”.
0-1 is balanced, but since you don’t get 0, it’s unbalanced then. Averaging on unbalanced distribution is biased sometimes, there exists better calc of APS to avoid score shifting, e.g. Using walson score lower bound for each bot instead of some 40 window moving average.