Hello,
1/ Please try to disable all the third-party plugins (including cache plugins), that does not come bundled with XStore https://xstore.helpscoutdocs.com/article/36-included-plugins , clear the cache of the browser, and check then. Maybe one of the additional plugins is the reason for the problem.
Let us know the result.
2/ What exact type of emails did you test? Because we do not see the problem – https://prnt.sc/3cearDdHsSJs
Regards