i spent so many hours watching logs of tests with my own custom PoW design years ago i saw all kinds of patterns as i altered the algorithm and parameters.

this is just the pattern of bitcoin, every 2016 blocks it readjusts and it tends to overshoot in both directions alternately, even if the hashpower doesn't change. it's like a thermostat, because it's a linear adjustment, it doesn't use a derivative factor, which reduces the overshoot.

i discovered that by meshing together 9 different block time targets, each double the previous, and having them all target an average as well as their own individual target, that i was able to make it both react fast to a rise in hash power as well as stay smooth.

later experience at energi.world i experimented with a super tight PoW they designed to be based on locked tokens, like a temporary staking to let you mine, that a standard single interval block timetable can either be smooth at changing or fast at adapting, and the smooth adjustment can lag badly behind hashpower changes, whereas the fast adjustment was really noisy, over and undershot all the time.

bitcoin's adjustment and schedule is basically in the in-between zone, quite goldilocks, but always you will see each adjustment period it will be longer, and then shorter, and then longer, and then shorter, the change depending on how much hash power rises and falls during the window.