SBE not sending emails - sent log shows "User content empty"

The Subscribe by email is not sending out daily digests, though the test email goes out just fine.

Cpanel error log has nothing.

Recipient spam folders checked - nothing.

The sent log shows that the email was sent out 3X, instead of once, but all logs show "user content empty"

Site info:
Uses Genesis Framework & custom child theme
Plugins that might interfere:
W3 total cache