The version of libssh2 shipped with PE 2021.5 and 2019.8.10 contains a bug that can cause segfaults, crashes, or coredumps during environment deployments.
Version and installation information
PE version: 2019.8.10, 2021.5.0
As a workaround, try disabling ASLR. If that does not resolve the issue, re-enable ASLR and open a Support ticket to get an r10k upgrade package.