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Disable the Time to SLA app.
Take a backup of the Database. Execute the following SQL query(change according to the DB that is being used).
DELETE FROM "AO_C5D949_SLA_MIGRATION_RESULT" WHERE "ENTRY_TYPE" = 'MIGRATION_STATUS'Re-enable the add-on and wait for it until it finishes the migration.
If the issue persists, please go to the "AO_C5D949_TTS_SLA" table and look at the "PROXIED_SLA_ID" column.
In that column, search for the value that is equal to "null"”. You'll be able to see the problematic SLA.