Well, here goes a couple of thoughts and ideas. Some of these may apply or none of them may apply.
POI Issues:
The majority of POI issues I have encountered with the Hogsters, Super Hogsters, and Super Yoters is due to the thermal being mounted too far back. On a Hogster or Super Hogster with their Tactical QD mount I would recommend at least 3 slots in and that is even stretching it. With their compact design, people tend to scoot them way back (even on ARs). I just talked to my fur buyer who's SH is not holding zero. When I asked him what rail slot, he had it on the very last one. It is barely hanging on the gun. There isn't enough rail to hold consistent POI. Tiny little shifts cause a lot of movement downrange.
Now on to the SY. The LaRue mount is very nice on the SY. However, it has a brand new design that doesn't feature a standard rail post. Good or bad, this means it has to be even further in. I have mine 6 rail slots in. I believe in my review and since I have mentioned make sure the entire length of the rail is supported. This is one of many reasons why I have a riser extension on both my AR and my bolt.
I do have one gun that seems at times to wander slightly. I believe it is due to the rail. It is never very far off. What I found is on this gun, if I simply re-seat the QD mount before shooting, my zero is back. I can't explain it but I have mentioned it to others and a few people have found this to be true. This is showing something on the rail is again keeping the mount from being able to stay in the exact position. The LaRue is so good at keeping zero, on this gun I simply open, seat it, and close, and my zero is perfect again. I really can't blame the mount as it happened on my SH and the SY, so it must be an out of spec rail or something.
Other things already mentioned is the mount being too tight or too loose. It is amazing how many people I talk to that say their POI is changing and when I ask if they adjusted their tension to their rail, they didn't realize they could. I realize this is not the case here, but just stating in general.
Also, if a person makes cam tension adjustments, the POI most likely will shift. It grabs and holds to the rail differently. If moving it from gun to gun, I would write down how many adjustments clicks left or right you do from gun to gun. It won't be massively different, but every minor change on a QD mount has an impact. In a perfect world, find a cam adjustment that works well on all your guns and leave it. I am starting to believe that over-tightening is just as bad as under-tightening.
Missing Coyotes: I believe there are multiple reasons this can and does happen even if the POI isn't the issue with a thermal scope.
One of the biggest reason is "height above bore". Many people use a 1 or 2" above center zero at 100. They say things like I've been doing this with glass scopes for years. Put a 3" above bore setting into a ballistics calculator vs 1.5" and you will see quickly it puts the flight of the bullet too high through the majority of the main kill distances for coyotes. There is no reason to set yourself that high for the majority of your shots just to try to shoot the occasional 300-400 yard shot.
I used to be one of those that zeroed 1" high at 100 with my flat shooting 22-250 because it is what I've always done. I then would then compensate by holding low on coyotes. I did this for so many years that when I get in a rush, my brain still does this at times and I have a tendency to aim low on coyotes in the 100-150 yard range. I am trying to retrain my brain as I now either use a dead-on at 100 or at the most .5" high at 100.
On top of this you add many coyote hunters sit/stand elevated. The greater the degree of elevation also aids in shooting high. Lots of coyote hunters shooting over coyotes.
Then there is the opposite effect. Many hunters under-estimate their yardages. Especially with the Super Yoter at 3x base mag and PIP. They swear the coyote was 150 when in reality it was 300 and they shoot low. When you can see the coyote so clearly and at times at such great distances, they simply aren't patient enough.
Zeroing: I am a huge advocate in aim small, miss small. I don't use any objects that bloom. I also shoot off my tripod. I have seen too many guns (yes free floated ones) that shoot different off bags, sled, or a table than off tripod. Also, this should be obvious but always zero at the same distance.
The SY does allow zero incremental changes of .54", .27", 18" and .14". In general they seem to work. However, I have experienced some odd anomolies where an adjustment seemed to be more and sometimes move it a few and it doesn't seem to go. I have gone to only setting the adjustment on 1x. At .54" increments, the most a person could possibly be of is .27". The zero movements seem to work better when setting them at 1x. I use 2x zoom on my SY when testing my zero. This is the max zoom I ever shoot, so this is what I use to zero.
Varmninter 223, some of these things may apply or maybe none do. DoubleUp is a good example. He went to great lengths to make sure he had every other variable taken out of the equation and then bam, his POI shift went away. There are so many things that can impact accuracy including the changing temps. I don't mean shift due to the SY in changing temps, I am talking about gun powder, barrel harmonics, etc.
To answer your question Varminter, I do check my POI on a regular basis. Have I ever changed my values. yes, by maybe 1" here or there. However, my guns take a beating, and I shoot lots of coyotes so lots of rounds go through my guns. A good cleaning, and usually I am back to where I was. Write down your coordinates. Just as a test case, take off the Super Yoter, and mount it back to the same rail slot, and see if your zero is back to where it should be.