Yes it does seem to solve my issue but I do not know if it is a statistical solve or a systematic one.
It would be pretty bad if I just “get lucky” now but the interrupt could still run into the problematic task.
If the interrupt was only able to produce the faulty behaviour because the printf gave room for a context switch or something like that it is an actual bug of the TCP Stack code which would be solved through the removal.
I tried debugging that but apparently debugging in this situation screws the timings to much for me to reproduce it accordingly.