There is a difference between the point and the end of the line
Visual artefacts when drawing thick lines
Answers approved by DevExpress Support
[UPDATE] In v15.1 and later versions, set the LineSeriesView.LineStyle.LineJoin property to Round to improve the resulting Line Series layout.
[Original reply below]
Hi Eric,
This behavior is by design. The XtraChat suite is using the DrawLines method to draw a line. Please review the sample in the attachment. It's illustrating the DrawLines method behavior in a similar situation.
To overcome it, use a line, which width equals one pixel.
Thanks,
Andrew