[racket] SIGSEGV MAPERR si_code 1 fault on addr 0xb7600000

I have an app recently deployed on on Amazon Linux EC2 instance.
Running an xecutable made with raco exe. This is 5.0.2. (Looking
forward to 5.1 soon!)

Basically it's acting as an SMTP server that relays to Amazon Simple
Email Service but when that fails will retry with another normal SMTP
server. The "main loop" is much like what's outlined in "More: Systems
Programming with Racket".

It writes some output that gets redirected into a text file for a
simple log. It's been up and running for 24 hours plus, working great,
processing 850+ emails. But I just came back and found in the file:

SIGSEGV MAPERR si_code 1 fault on addr 0xb7600000

Gah. And I'm realizing I don't have a great idea how to proceed. Does
anyone have any tips or clues or advice?

Thank you.