Tasks run constantly in a loop

I have 2 tasks on one site scheduled: one daily and another weekly. Recently they started to run continuously every 5 minutes, nothing changed in their schedule. Both workflows are manually started and just 1 action to send an email with notification. SP 2013 version.
After the first incident, I just deleted the tasks and recreated new ones - that helped for 2 days they were running as expected, but then it happened again. What it might be?