If the 500 error is intermittent, then it’s likely your account is hitting the memory_limit for the account.
To increase this, see the following…
How do I change PHP versions, or change my PHP settings / config?
Then please set memory_limit = 512M
If that doesn’t help, then we would recommend checking your PHP error logs…
I am getting an error on my site. Where can I find my error logs / error_log files?