Seat selection on Transavia segments
 

I made a booking with KL which includes a segment operated by Transavia. I can't select seats on KL's website because apparantely their systems are not connected to their own subsidiary, and I can't select seats on Transavia's website because the ticket is on KL stock.

Is there any workaround or do I just wait for check-in and hope to not end up in a middle seat?

Unfortunately you have to wait until check-in

Thank you. I'm still within the 24 hours window so I'm just gonna cancel and book something else. Quite bizarre given that both airlines are part of the same group...

Indeed.

They really managed to make Transavia the best of both worlds: the price of AFKL with the service of LCC

Had this same issue on a recent booking, neither KL or HV call centres were able to assign a seat for me (KL flight number/ticket on an HV plane). KL did give me a separate PNR for HV, which didn't work on their web-site but has worked on their app! From there, I can select a seat, although all seats are chargeable unfortunately (despite being Flying Blue Plat).

Beware that it's useless even in their app. You can see the seat map, you can try to select a seat, but it won't allow you to purchase a seat.