Migrate from Snort 2 to Snort 3
Starting with Version 7.0, Snort 3 is the default inspection engine for new threat defense deployments with management center. If you are still using the Snort 2 inspection engine, switch to Snort 3 now for improved detection and performance.
Upgrading threat defense to Version 7.2 through 7.6 also upgrades eligible Snort 2 devices to Snort 3. For devices that are ineligible because they use custom intrusion or network analysis policies, manually upgrade to Snort 3 as described here.
Although you can switch individual devices back, you should not. Snort 2 will be deprecated in a future release and will eventually prevent threat defense upgrade.