I have a couple of entries that I added into my system crontab file a while back that I noticed immediately working. I’ve been running the command manually for a while because I couldn’t be bothered invetigating. When I did sit down to investigate, I found that running:

crontab /etc/crontab

Makes crontab echo the output to STDOUT. Including errors. It’s kind of annoying how those errors don’t appear in my system message log normally, but at least I found the error! The error – what looked like wordwrap wasn’t, and so crontab was seeing a syntax error