Hangfire Processed Old Records

Hangfire processed old (already processed) and new records (records to be processed) at once.
This iteration it took around 4 minutes to process (this is the only clue). Normally it is taking around 500 miliseconds to be processed.
This is happening only once yet but is this a bug or did I miss any configuration? Any feedback is appriciated.
Due to this there are lot of unwanted emails were generated and trying to stop happen that again.