Repetitively emailing old lab group about a paper constantly on the backburner
It's naturally to everyone's benefit to get the paper published. However, it may also be the case that your former PI and co-workers may not have the time and focus to work on it themselves.

Perhaps the best way to get things moving again is to change your question. Instead of asking a variant of


  Will the paper be submitted soon?


try asking them what will help them:


  I know you're very busy. What can I do to help get the paper submitted?