Not seeing any reasons why this wouldn't simply be a E. Pied, which occasionally show narrower tertial edges such as this - see:
ML267277161 European Pied Flycatcher Macaulay Library,
ML480155831 European Pied Flycatcher Macaulay Library. Primary patch perfect for Pied, while 2nd wing bar is normal for 1st winters in all 3 sp.
Semicollared is usually paler and greyer on upperparts and with slightly paler centres to wing feathers and uppertail coverts, so overall a less contrasting bird.
Anyways, definitely not an easy group and worth trying to get a voice recording next time you face an interesting bird.