I am having a very frequent occurrence (although not always) of setting a vim marker and when I go back to it, it goes back to a previous marker location.
For example, I type mm to set marker 'm'. I see the green marker icon on the line in which I set it. I then navigate to another location in the same file and when I am finished, I press `m to go back to the marker and it goes back to an older location of the 'm' marker. When I go to the last place I set it, the marker is gone.