Harmonic sequence
When you encounter a chord progression that acts as an exception to the harmonic function flowchart it may be because it’s actually a sequence but for the chords.
Example
- I -> V is normal
- Movement: a 5th up
- V -> IIm is “weird”
- Movement: a 5th up
- IIm -> VIm is “weird”
- Movement: a 5th up
So then ii -> vi is I -> V sequenced up a 2nd!
For examples from real songs, see: https://musictheory.pugetsound.edu/mt21c/ExceptionsCreatedBySequences.html