Varnish is a tool that is used by web servers to cache data, therefore making sites load faster. Most of the time it works amazing, however it can occasionally cause problems.
You will need to talk to support and ask them to make a Varnish exception for https://example.com/?cf7pp_redirect – where example.com is your domain name.
Hosting companies know to have problems include WPEngine and CloudWays, however this list is not exhaustive.