For some reason, I have found nothing about this issue except this thread. It definitely worked prior to the upgrade to 24.7, and absolutely does not in 24.7, at least when I tried it last week.As noted, I downgraded to 24.1.10, and it's back to working, but I was able to do so by rolling back to a snapshot.One tip: If you downgrade manually to 24.1.10, make sure you have a config file ready that was created in 24.1.10 or earlier. At least in most similar setups (and I assume OPNsense is the same way), restoring from config only works if the config file was created from the same or earlier version to which it's restored.Of course, downgrading is only a temporary solution. It's not feasible to remain with 24.1.10 permanently, so hopefully there is some interest in a workaround or patch in 24.7 for this, because it's beyond my technical skills to fix it on my own.
This recent post may shed some light on this issue: https://forum.opnsense.org/index.php?topic=42552.0.If WAN cannot ping remote hosts in 24.7, that could explain why gateway monitoring is broken.For those of you who have 24.7 installed (as noted, I rolled back to 24.1.10 due to this problem), I would suggest manually attempting to ping from each public-facing interface (WAN, WAN2, etc.) to 8.8.8.8 or some other remote host to determine if that's the source of the problem.