I also have the v5.1.9 of EBD, and the latest WP installation (5.4.1).
I see these 2 errors in the Site Health Check (xxxx/wp-admin/site-health.php), on these 2 sections (my WP is in French, so here is my translation – maybe inaccurate – of these sections) :
Section “Critical issues”
Title : 4.91 The loopback request to your site failed
Details : “…… error : cURL error 28: Operation timed out after 10000 milliseconds with 0 bytes received (http_request_failed) ”
Section “recommended improvements”
Title : Background updates not working as expected.
Details : “…… _ “wp_version_check() is unavailable” ”
Is this helping you ?