Resurgence of people using third-party programs to find hunt marks?

[KageTokage]

These tools do exist and players use them all the time. In fact, ACT has a feature on it that does the same thing with the use of triggers. These triggers are posted on FFXIV reddit and most ACT users use them. (Parse programs can do a whole lot more than parse). From the description of the triggers, it calls out any hunt regardless of rank when you reach a specific amount of yalms to the target. It's most probable that ACT triggers are the radar that these suspicious individuals are using.

ACT isn't able to tell the exact location of a hunt, only if it's present in the zone somewhere.

People have been using an offshoot of Guildworks client that was popular in the 2.x days to automatically ping them the location of S ranks so they can find them immediately even in zones with lots of obstructions that prevent you from spotting them until you get close.

As I mentioned earlier, there are people who subtly stalk me and others in my hunting linkshell, lingering around in zones where they see us being active and insta-calling the S ranks as they're spawned. Which wouldn't be an issue if there weren't players with a tendency to immediately pull said S ranks, sometimes resulting in them dying before all of us can even get there.

TLDR; lazy players with hunt detectors are causing harm for the people actually doing the hunting.