In Jain doctrine, the cycle of time is divided into utsarpini (ascending) and avsarpini (descending) halves. Kevalin (one who has attained kevala jnana) are liberated souls who have shed all karma and do not stay in the world after enlightenment; they remain liberated.

There is no universal scriptural rule that forbids new kevalins from arising during the current avsarpini. In fact, kevalin jnana can be attained by deserving souls within any avsarpini by following right knowledge, right belief, and right conduct, and by shedding karmas. The tradition does not prescribe a fixed halt on the appearance of kevalins until the next avsarpini. Different Jain lineages (Digambar and Shvetambar) may emphasize different details about who attains kevala jnana and when, but the core idea remains: kevalins come when a soul fully purifies and uploads kevala jnana, wherever that soul is in the cosmic cycle.

If you have a specific source or tradition in mind that uses the phrase “no new kevalin until next avsarpini,” I can compare it with canonical Jain teachings and explain the exact meaning and context from Digambar and Shwetambar perspectives.