Q:

How does flexible casting interact with itself? 

As I find builds about the Coffeelock (for peoples who doesn't know, it's a build that hollow you to have an infinite amount of 5th level spells slot RAW, involving a sorcerer multiclassing in warlock), I turned out asking myself a question:
How does flexible casting interact with itself? 
To be clear, I want to know if you can turn created spell slots into sorcery points RAW (which could mean you have an infinite source of sorcery points if you need to do metamagic with your infinites spells). 

A:

The flexible casting ability has no memory of where the spell slots came from (until you go to sleep).1
Flexible casting simply states:

You can use your sorcery points to gain additional spell slots, or sacrifice spell slots to gain additional sorcery points. 

So sure, you may burn slots created from sorcery points to get sorcery points.  Note, this always results in a net loss of resources.  I expend 7 sorcery points to gain a 5th level slot, then burn that slot to gain 5 sorcery points.  Spell slots always cost a greater number of sorcery points than the slot's level, but a slot can only return a number of sorcery points equal to the slot's level. 

1Flexible casting does specify, "Any spell slot you create with this feature vanishes when you finish a long rest."