Your staging server does not use WPE's caching technology, which your production server will use. WPE will not give you details on how their secret-sauce caching works. This means that things that work on staging will break on production. WPE also refuse to turn off their caching on production, but also refuse to turn ON their caching on your staging server. This means there is no real way to test. Things that work with their staging server, and even work with the standard WP caching plugins, will break in WPE production.
Their solution? Buy another production site to test on.
That website is now moving from WPEngine after having its launch botched by the aforementioned issues, and after not being able to make a basic paywall work with their caching. Once they realised the use case, WPE simply suggested moving elsewhere without making any further effort to accommodate.
I had a similar reaction to the post yesterday by asmartbear as Jaques, but he made the extra effort to actually write the blogpost, so bravo to him. WPE enjoys this sterling reputation that misleads a lot of people into using them, but their comfort zone it seems is limited to vanilla WP installs with little deviation.