Assertion fails while freeing IOBs.

I constantly get the following assertion to fail:

`mm/iob/iob_free.c:100`

```c
/* Copy and decrement the total packet length, being careful to
* do nothing too crazy.
*/

if (iob->io_pktlen > iob->io_len)
{
/* Adjust packet length and move it to the next entry */

next->io_pktlen = iob->io_pktlen - iob->io_len;
DEBUGASSERT(next->io_pktlen >= next->io_len);
}
```

At least for me, the failure seems to be triggered while I am using a custom TCP server (mostly when connections are closed).

I haven't been able to find any specific commit that is suspicious.

Unfortunately, I am also not able to reproduce the issue reliably.
It randomly happens, sometimes almost immediately when connections are closed, sometimes everything seems fine for extended periods of time.

I would appreciate any hint as to what to look for to fix this.

---

As a reference, this is the stack trace at the moment of the failure:


*(Moved from the apps repo, [where](https://github.com/apache/nuttx-apps/issues/1562) I accidentally opened the issue.)*