503 error on export

Plugin has worked like a charm until recently. Every week I use it to export a specific custom post type published within the last seven days to a CSV, but recently when I go to export I receive this error:

Error 503 Service Unavailable
Service Unavailable
Guru Meditation:
XID: 1788511856
Varnish cache server

I disabled varnish plugin to see if that was causing the error but it still doesn’t work. Our hosting company believes it is being caused by some sort of PHP error and not their servers.

Any thoughts??

https://wordpress.org/plugins/wp-ultimate-csv-importer/