This should be comment but im unable to fit this message in comment size limit -w-

Are you watching entire address space or address region of ART's java heap? my speculation is your userfaultfd interfering with GC on ART (Android RunTime) VM. Android 13 replaces the GC with one using userfaultfd for improving various stuffs and it also got backported to Android 12.

Because i cant see the code, i dont know for sure. UFFDIO_REGISTER can return EBUSY if overlapped with other one watched by ART VM so if i is indeed ignored by your code it leads to that issue.

See https://en.wikipedia.org/wiki/Android_version_history#Android_13 and https://man7.org/linux/man-pages/man2/uffdio_register.2const.html#ERRORS