When I set yDomainRange's maximum to 5996.099999 in the barchart, the gridline for 5000 disapeared. The issue resolved itself when I changed yDomainRange to 5996 or 5997, so I am guessing that the issue is caused by setting the yDomainRange to a non-integer. I was able to fix it by using Math.floor to correct the number. Although it seems like a strange number to set yDomainRange to, it can happen if you are calculating it based on the values in the barchart - I was using maximum value * 1.15 to leave a little space at the top of the chart. Just thought i'd share this, so even if you decide not to fix it the next person with this problem might be able to find my solution when searching through issues.
When I set yDomainRange's maximum to 5996.099999 in the barchart, the gridline for 5000 disapeared. The issue resolved itself when I changed yDomainRange to 5996 or 5997, so I am guessing that the issue is caused by setting the yDomainRange to a non-integer. I was able to fix it by using Math.floor to correct the number. Although it seems like a strange number to set yDomainRange to, it can happen if you are calculating it based on the values in the barchart - I was using maximum value * 1.15 to leave a little space at the top of the chart. Just thought i'd share this, so even if you decide not to fix it the next person with this problem might be able to find my solution when searching through issues.