After upgrading a host’s operating system we ran into this error on a Magento site:
There has been an error processing your request datefmt_create: no such time zone: 'UTC': U_ILLEGAL_ARGUMENT_ERROR
After much debugging it turned out that the version of ICU inside the PHP-FPM chroot had not been updated.
Updating the chroot copies of the ICU libraries resolved the problem.
Hope this helps someone else get to the bottom of this quickly!