In OpenBSD 7.4 before errata 009, a race condition between pf(4)'s processing of packets and expiration of packet states may cause a kernel panic.
https://github.com/openbsd/src/commit/9d9f4dc6c833cb79d13f836581e3a781d06842e7
https://ftp.openbsd.org/pub/OpenBSD/patches/7.4/common/009_pf.patch.sig