With V2 I've noticed that when using the Freehand Selection Tool in Polygonal mode the selection lines temporarily disappears if I pan around the canvas. If I wiggle my cursor/stylus it reappears after 1-2 seconds so it's not a huge deal, but it can be a bit annoying at times.
The long explanation: When you are selecting in polygonal mode then you can lift your stylus/mouse to reposition before continuing the selection (unlike the freehand mode that automatically closes the selection when you do the same). When I do this and press spacebar to pan around before continuing the selection the selection guides (not the marching ants) vanish temporarily so I can't see where I left off last. They reappear after a second or two or when I hover my Wacom pen around a bit, but I've never had this happen with previous versions of Affinity. This happens with my mouse too.
I thought it might be a known bug and would be addressed in 2.1, but no luck!
I can reproduce this time and time again, so if you need a screen recording for clarity I'm more than happy upload that here.