Hey,
The thing that took significantly longer than usual, was the opcache being cleared. Without this, what happens is exactly what you are describing (segfaults when invoking occ and on other occasions). Did you maybe abort it accidentally?
You can run the opcache clear script again with the following commands - maybe that will solve the segfaults:
sudo bash -c 'source /usr/local/etc/library.sh && clear_opcache'
sudo service php8.1-fpm restart
EDIT: The 503 errors during the update are a big oversight by me, sorry for that! You should be able to fix it with sudo service php8.1-fpm start. Alternatively you can wait about 2-3 hours and run ncp-update again. Until then I should have fixed it