Check your DBConnect Connection Health from the DBConnect App to make sure connection status of the DBConnect App.
Is your dashboard running searches against Indexer or database? If it's from Indexer, make sure DBConnect is configured to ingest required data only from the database, and also use specific index table if your DB Input have larger data set.
Have you checked the cron schedule for the DBConnect DataLab? Also, is DBConnect app showing any errors?
We had an issue where the port used by DBConnect was not running and so it had stopped executing the data labs.
The dashboard running slowly should not be related to the DBConnect application as it will be fetching events from the Index and not the app. You might want to check if you have any performance issues on your Indexer(s).