This is a problem I have occasionally since I've been using snapping, but I'm using it a lot lately, so I get it way too often:
no matter if I am using the moving tool or the polygon tool, there's a point when the snapping decides to snap far from the target model, as in the picture:
the selected point is far from the surface it's supposed to attach to, and no matter what I do, I cannot make it connect to it unless I turn off snapping.
once it happens it just keeps doing it.