A "little" late, but I wanted to provide some insights for everyone, to learn / improve nonetheless.
The mentioned hesitation did not leat to a fatality, I am still alive and came out of it with just some bruises...
After opening I recognized a flip-through malfunction, which was caused by myself due to packing directly on a field after an outside landing the jump before. In hindsight, I could have most likely landed it without issues, but in that moment decided otherwise as the canopy above me was not "good".
As practised, I grabbed both handles with one hand. I pulled my right hand until full arm extension and tried to pull my reserve handle after that but I was unable to pull the handle at all, it did not move even a little.
I turned my head to the left and saw my main still attached by something and my reserve pilot chute being out. My first thought was, that it might be that I did not pull the cutaway cable all the way, so I cleared the cutaway cable from the housing completely.
But I was still hanging from my main by something I could not identify in that moment. I instinctively grabbed that thing from what I was hanging, tried to pull up and just before I wanted to pull on my reserve bridle to get my reserve out, the hangup cleared.
I saw and recognized that I was no longer attached to my main but due to my body orientation and possibly low speed, my reserve could not be extracted.
I turned back to my belly and waited for the reserve to come out, which it thankfully did after a moment.
Basically my reserve cable and pin was not able to pass the RSL ring to which the extension cord was attached. It looks like the edge of the pin got stuck at the back of the knot of the extension cord and due to the tension locked there. So I was still connected to my main by my reserve cable and RSL. I just grabbed whatever I was hanging from and thankfully the pin cleared the ring possibly due to me grabbing the pin or releasing some tension.
Trying to find the root-cause for this incident myself, I also tried misrouting the reserve-cable through the knot, but this does not happen easily. You have to put way more effort in misrouting it, than in doing it the right way.
In the end, Sunrise Manufacturing issued this service bulletin for it.