I have a Samsung Galaxy Tab S2, running Marshmallow. For some reason, when I use my bluetooth keyboard, I get an intermittent error when pressing space (or any punctuation). As near as I can tell, when it does happen, it is when I press space after a mispelled word (or one which is not in the dictionary) or a number. When it happens, it moves the cursor to the beginning of the mispelled word.
For example, if I type '2017', then hit space, the cursor will jump to the beginning, like so '|2017'. As you can imagine, this is incredibly annoying. When typing my email address, it jumps 3 backwards times.
I know this is incredibly specific, so there might not be an answer. If I remember correctly, it may have started happening when I added another language to the on screen keyboard, but I've disabled that and the problem remains.