I'm very grateful for your advice.
However Stephen comment disregarded the important information on my email.
As I have said before, I have two applications. One acting as client one as server.
The client application does have misplaced lwip calls which I'm trying to remove.
The server application does NOT have lwip calls from within interrupts, and that's where my problem is.
As you can see from the pcap the digest challenge is sent to the server side but the server does not process it and sends a RST.