Hello Didier. I know what you mean, sometimes snapping gets kinda wonky and things don’t snap the way you intend it to, as if Blender is being a trickster and is laughing behind your back.
What I like to do when that happens is reset the whole thing, so check the scale is 1, 1, 1, just in case, recalculate your normals, so Shift + N the whole mesh, the origin point if it’s out of whack set it to the object center again. I don’t know if it makes any difference but I like to set the objects location to round numbers, so the X, Y and Z values in the location I avoid it having long decimals. One that works most of the time for me is changing the “Snap with” mode to “Active”, so things will snap to my active element, in this case the last vert I selected. Most of the time this little things work out, but then sometimes it doesn’t and I go for the nuclear option, I separate by selection the part of the mesh that is giving me trouble and work on that piece detached like that or delete it altogether and remake that part separately just so snapping works correctly again.
Hope this helps.
