I think this bug was introduced a few versions ago:
As you can see in the gif, from a zoom level and above the items do not snap to the visible grid but snap in unpredictable places in between grid lines
I think that problem is still there. I was just fighting with it last 3 hours and finally I have found this info here.
In few songs all seems to perfect. In one just one MIDI file (5 on one track - all working fine) I can't move notes other way as it will snap to the invisible grid.
Would no quantize either. It's small 20 notes file but I can't do anything with it, while other files on the same track are quantizing and can be moved manually, single one or all of them anyway I want to.
But I was fighting with that particular file (or take) for 3 hours not knowing that others are working fine. From one early song I have copied all settings regards snap and still nothing. So I'm here and most is working for me except that one old take.