When you install ModSecurity3 via the experimental repo, this will cause ModSecurity Tools to stop reporting the ModSecurity rules that were being hit.
We've opened an internal case for our development team to investigate this further. For reference, the case number is CPANEL-35339. Follow this article to receive an email notification when a solution is published in the product.
The Apache logs still log the occurrence of ModSecurity hits on the server; you would need to review the /etc/apache2/logs/error_log for what rules are being hit and for what domain.