I believe it's similar to the Alps EC11 and the Bourns PEC11L series, both I believe available from Mouser. It's 15 pulses per revolution, and 30 detents per revolution. But I never found one that didn't have a shaft that was way too long. I'm sure the JYE encoder is a no-name item. There isn't a mark on it.
But before you spend money on a replacement, you may want to try taking yours apart and cleaning it. That's what I did, and it works fine now. No guarantees of course, but you can bend up the four little tabs holding the metal plate to the green plastic, and it comes apart. In addition to cleaning it, I bent the contact arms up just a little so they would press against the disk a bit more forcefully.
Mine behaved very erratically, but now works fine. I never did see what was causing the problem, but the process worked. You have little to lose trying this. You can always order a new one from JYE, or order the PEC11L from Mouser and cut off the shaft. But I suspect you can make the existing one work fine. The hardest part is desoldering it from the Shell, but you'll have to do that at some point anyway.