I see it shows only with some particular Y Size of the canvases. When you resize the window along Y it is alternatively good or bad.
By the way, retina or not retina is the same.
I am looking at it and also at something else at the same time. I did some progresses but still do not have fix. I am on the other problem now… also no obvious fix. I’ll let you know.
Because of some other problem (Spherical harmonics) taking a large fraction of my time I was not able to come back to this. I made a Jira report with your request to better keep track of the issue and to summarise what I already found in order to ease the come back to it: sft.its.cern.ch/jira/browse/ROOT-6561