When clicking on "Run Discovery" button on a Service Map, the "Starting discovery" message pops for a few seconds, then disappears. Discovery does not seem to start.

After clicking on "Run Discovery" button on a service map, the Service Mapping engine checks sa_endpoint_status table to see how many jobs are running.

If count of jobs is more than the value of system property "sa.max_concurrent_service_discovery_tasks" (if set), or 100 (if the property not set), then discovery won't start.

This issue may be caused by a large map that's being discovered.

You can check sa_endpoint_status to see the count of records that are not in Completed state.

You may open Service Mapping > Service > Application Services, then filter result with "Discovery Status" not Done to confirm which Service is still being discovered.

Review the large map, and mark unnecessary connections as "boundary" so they won't be discovered - check below doc:
Remove CIs not belonging to application services

Other options are:

1> Stop Discovery on the large map that's running
2> Change service discovery schedule starting time to after hours
3> Create or update system property sa.max_concurrent_service_discovery_tasks and set it to expected value (default is 100, increasing this will have impact on performance)
4> Create or update system property sa.rediscovery.batch_size to 150 (this will make Mapping Discovery faster with sacrifice of a bit performance, default is 100)