Changing and tuning default alerts suppressed by lowering severity, wait cycle or symptom changes, all these changes were gone after aria operations upgrade
VMware Aria Operations
All customization on default content was overwritten by upgrade process , this is done as per design
As per best practice customer is advised to clone all default content and create the custom one as any default content is always rewritten during any upgrade
Installing and Upgrading VMware Aria Operations
Upgrading to VMware Aria Operations 8.18.3 or upgrading any Management Pack (MP), resets out-of-the-box content as part of the software upgrade process. This implies that the user modifications made to default content such as alert definitions, symptom definitions, recommendations, policies, views, dashboards, widgets, and reports are overwritten. You need to clone or backup the content before you upgrade to VMware Aria Operations 8.18.3.
This is valid for all versions of aria operations
There is no way to restore this unless you still have snapshots, backups or content backup Creating a Backup