As mentioned in the original post, I was running 13.17.0.
That said, I'm on 13.17.2 now and haven't had a crash yet. BUT, I've intentionally spread the extensions to a couple other servers, as to lower the load, which lowered the crashing frequency to once a week, then lowered it more until no crashing for about three weeks. Still had another crash about three weeks later.
Since on 13.17.2, we haven't had any more, but it's only been about a week. I'm going to move all the extensions back over to the one server and see if the increased load causes another crash on this newer version of Asterisk.