Long drush call causes an infinite loop, when not using ingest sets.

The drupal timers are not reset when one is "started", so once you have used up 2/3 of the lock timeout. 

It tries to re-schedule it, except because we are re-using the same lock name then the first check still sees the previous runs time. 

So you are already over the 2/3rds of lock timeout. Rinse, repeat, ad infinitum. This just clears the time when you re-schedule.