Following the steps on this forum thread allows one to reproduce a behavior where the grid columns display is broken. Notice the related example has a Viewport with RTL="true" properly wrapped.
GridPanel Horizontal scroll on columns resizing with RTL orientation Chrome Only.
There's a very similar Sencha issue here: First column of gridpanel cut when its region is center in RTL only
Issue could no longer be reproduced in Ext.NET 4.2.0 with ExtJS 6.2.1!