Incidents would not get raised from alerts.
This is because job "Event Management - Evaluate Alert Management Rules" would not execute. This is responsible for triggering alert action rules.
This problem was observed in a multi-domain environment where the jobs were defined with a user who is not part of "Global Domain".
In this case, all the Event Management jobs were defined by "Event Management" user, but the job: "Event Management - Evaluate Alert Management Rules" is touched/modified by some user called "System Administrator"
This user "System Administrator" is not part of the Global domain as you can observe from below screenshot.
Update the job so that it would be part of "Global Domain" with "Event Management" user as "Created by. You may recreate the job in Global Domain.
You may contact ServiceNow support if you face any problems following the KB.