Please go to the Dashboard of WP Enginge (that is not the wordpress dashboard) and navigate to the cache Exclusions rules. There you will have the option to chat with a customer service person. Ask this person to apply the following rules:

path: ^\/wp-json\/splitTestForElementor\/v[0-9]*\/.*

path: ^\/split-test-for-elementor\/v[0-9]*\/.*

If you are doing page against page tests please make sure that you also ask that the tests urls are also put into the exclusion rules.

You can get more information on this here: https://wpengine.com/support/cache/#Cache_Exclusions