After 7 months with no SSR drawn, I've changed the way I draw Jewel Gacha. I'm taking them 1 at a time, never 10, and always at server quiet-times. Since then, I've drawn 2 SSR, which is roughly the right proportion (first 18 months playing, 22 SSR Eido and 20 SSR Kami; roughly 1 SSR every 2 weeks; switched to 1 at a time off-peak 4 weeks ago).

There's something called "running out of entropy" that can happen to busy servers that use random functions frequently. It can cause a significant change in drop rates - if a Linux server runs out of entropy, all random numbers generated are zero until new random seeds are generated. Recently learned about this in my new job, and am wondering if this is a thing in Kamihime Project. It's just anecdotal evidence & theory though. If I cared, I'd try to get broader data - rates of SSR drop on draws of 10 and draws of 1 with a server time associated, see if there's any correlation. But that sounds like effort, I have no idea if anybody else here is interested and don't produce enough data myself.