There was no hint changing the default version to python36 Mk/bsd.default-versions has PYTHON3_DEFAULT?=3.6 when running Poudriere bulk builds with no python related in Poudriere's /etc/make.conf python35 is deinstalled and no python36 is installed, causing broken systems with python3 N/A.
(In reply to p5B2E9A8F from comment #0) There was no hint changing the default version to python36 in /usr/ports/UPDATING
(In reply to p5B2E9A8F from comment #0) Edit: After running Poudriere bulk builds with no python related in Poudriere's /etc/make.conf python35 is deinstalled and no python36 is installed when doing pkg upgrade on clients, causing broken systems with python3 N/A.