Hello, first of all I'm a HUGE fan of Affinity Designer, you guys are awesome :)
I have Ipad and Mac versions and this bug happens in both of them. I make a lot of seamless patterns and this bug is affecting my work real bad. I made a quick video to show you how the bug occurs and is very easy to duplicate the error, in my iMac and iPad pro this happens all the time.
When selecting groups of objects and using the Cmd+J duplicate command, after positioning the duplicate objects, one of the original just "disappears" from the screen, but when you look at the layers panel the object is there, but when clicking the object through the layers panel, the selection box is far away from the object. I just tried to use symbols for making seamless patterns and this bug makes it impossible to use.
My object in this video is a group of two pixels layers, but just tested with vector layers and happens the same thing.
I hope is some easy fix :) Thanks a lot!