There’s PD behaviour [while new seletion polygon drawing] exists about when you click somewhere out of image whole polygon tops already set just disappearing, which can be a good option if you made some mistake drawing it and want to get rid of it, however more frequently it causing much more serious problems - you just losing all of tops already pointed of some complex already almost allocated (i.e. to finish it you have to pin one more top near the image edge after connecting it with first polygon top pinned) selection polygon, that is clearly frustrating.
Most frequently it happening because you just don’t see the image edge and clicking somewhere near it just by guess, most frequently making mistake clicking outside an image that way cancelling whole polygon.
On screenshots provided you can see my tryout (that’s just example of tryout, there’s nothing really to select exactly on that image at that area) of drawing complex polygon near the image right edge, which, after me clicking out of the image when it almost completed, dissappears at full, that is unacceptable for one who make selection, as, I bet, frustrates her/him same much as me:
All that happens mostly because of image edges are just not visible because of have no any contrasted borders (except bottom one, that clearly seen as highlighted by bright [white?] line)
Good to be done if all the PD image edges would be contrasted by i.e. same white line as it already done at PD image bottom edge or [as an option] clicking outside of image would not lead to cancelling currently drawing [but still not finished] selection polygon - finally if you totally don’t like polygon created you can always just delete it by clicking a cross near selection polygon after it’ve being created and… selected.
That will free players who still playing PD from frustration because of “losing” near-the-edges selection polygon, and therefore will will increase the amount of processed data by the players (if to believe it really benefits someone in real life, evidence for which does not exist and many players (including me) have many doubt on it (i.e. here: Project Discovery 99% - #2 by Kimberley_Kuvakei)
P.S. it looks like almost the same (but not much detailed) issue which lead to PD result failure, already raised here 4 years ago ([Project Discovery] Edge detection issues), but that was some kind of totally different PD, but issue was still about ‘detecting image edges’.