This is an old problem that only triggers if all of the following happen at once:

• The request is handled by a specific PM web server
• A node on the page uses <spoiler> tags
• Inside of the <spoiler> tags are <code> tags
• The code is over 32kB or expands to over 32kB when expanded (maybe?) because...
• The viewing user has a complex "Code Prefix" configured (or similar)
• At least one other condition that I have not yet identified (perhaps related to how recently Apache has been restarted?)

And then what happens is that the Apache child dies due to "illegal instruction".

See also Re^5: "Invisible" nodes (details) (which includes an example thread that isn't currently failing for me even though I'm currently able to trigger the failure via other means).

Note that trying to combine all of those items together outside of Apache doesn't generate even a warning nor invalid results, even on the same version of Perl that Apache claims to have been linked against. Also note I've yet to figure out any way to get the failing case to tell me any hint about which of the many lines of code involved is where the failure happens (so I could just change it somewhat randomly so that it does the same things but just stops dumping core in that version of Apache).

In the mean time, I replaced a few uses of <spoiler> tags that weren't being used to hide spoilers with <readmore> tags so Cool Uses for Perl should load for everybody no matter which web server they hit (until the next person does that again).

Sorry for the inconvenience.

(Updated a few times in fairly minor ways after posting)