What type of post and what is it set in? Are they wood in dirt with no concrete? Are you saying that it is moving down vertically? Something hast make it move, or displace what’s under it. Maybe remove them one at a time and set them in concrete. Hard to help more without more info or pics.
Theyre all wooden posts, set in cement. I don’t know how deep though… We hired someone to do it. They are definitely moving vertically, but I don’t think there’s any wobble from side to side… The latch is locking, and it’s about two inches tall, but it is always in line in the y axis, it just goes off up and down. Not sure if it’s both sides moving, but I know the gate is now also hitting the cement holding the opposite post.
If they are moving vertically it sounds like the ground under them is subsiding. Either that or it’s being removed. Is the whole fence doing this or just one or two spots.
Looking at your pics, it looks there are underground valves right there. Check if one of those is leaking and the water is causing the soil to migrate away.