So, a little over 5 weeks (!) later and my portfolio has finally been transferred. Interactive Brokers kept me informed every step of the way via their messaging platform which was really great service (by no means do I have a large account).
Regarding their interactions with Degiro, Interactive Brokers summarised it as follows:
Unfortunately their process is very slow, complicated and not up-to-date
This echoes my experience as well.
-Mustachioed