A client gets the following error
CRITICAL: Uncaught PHP Exception Exception: "Could not gather sufficient random data" at /.../vendor/paragonie/random_compat/lib/random_bytes_mcrypt.php line 69 {"exception":"[object] (Exception(code: 0): Could not gather sufficient random data at /.../vendor/paragonie/random_compat/lib/random_bytes_mcrypt.php:69)"} []
[Corrected client PHP version]
attempting to view or edit a record. Client is on Symfony 2.8.2, PHP 5.6.18, running on freebsd. My development system is Symfony 2.8.2, PHP 7, Windows 10 and does not get this error.
Running composer update did not affect this behavior.
The answer appears here courtesy of Scott at paragonie. It says,
It means precisely what it says: Something about your environment is preventing mcrypt_create_iv($numBytesRequested, MCRYPT_DEV_URANDOM) from generating enough entropy.
Make sure PHP can read /dev/urandom, especially if you're in a chroot jail. Without access to the kernel's CSPRNG, we cannot reliably generate random data suitable for cryptography.
Since the site is on a shared host and I am largely freebsd illiterate, I forwarded this to the host's webmaster. Issue solved.