The case can be made that the reason the Flynn sentencing is postponed by Mueller's team is that they have a Giglio material issue and they are looking to run out the clock a bit.
Basically, in a plea, the government must disclose exculpatory evidence INCLUDING (as per Giglio) reputational issues of witnesses. Strzok participated in the Flynn interview, is married and having an affair, discussed modifying interview notes (called 302s), and was ultimately reassigned to HR desk duty from Mueller's investigation because of demonstrated bias.
Did Mueller's team disclose this to Flynn's team prior to the guilty plea? Well, if not, the plea can be withdrawn and good luck finding anyone to take that to court with what the public now knows.
Let's not forget this was an informal interview, that it was voluntary, and Flynn had no counsel present! And it was not recorded!
Can we get some informed discussion on this?