Any Chrome plugins/extensions installed? What OS version do you use, touch screen? Do you have opportunity to check it on different machine?
Support Forum
Please, add ?video=1
to the url with our online example: https://bryntum.com/examples/gantt/basic/?video=1
Click all to reproduce that bug, find FEEDBACK button on the right side and Submit the bug report.
We will have that report recorded by https://therootcause.io/ tool.
All the best,
Alex