Yes, I had sometimes your same symptoms with the "No free buffers for rx" messages and crash.
This happened in the debug phase when my application couldn't store/process all the received data. This was typical in a situation where I had another high priority task that blocked the network task for a sensible amount of time. I think the crash was caused by sgdma which kept on loading incoming data into memory, so generated an overflow.
In rare cases I had the same problem when application accepted the first connecion or when the debugger restarted the program after hitting a breakpoint. For these I didn't find an explanation.
I never tried if the same problem is triggered by a rapid connect/disconnect.