Well as I was recording and exporting, then importing this for the forth time it worked... I always did the exact same process, even exited Spriter after each try and now it worked. The .scon must've been a bit buggy for some reason, because I've noticed that the last time I exported the .scon with the SpriteSheet, it was 0.7kb larger than any of my last attempts. Only thing that was different is that I made a completely new directory for the exports (for the convenience of the video). There don't seem to be any more issues since that. Thank you for taking the time to reply!
About the browser versions; If I want to access a new version I just directly enter it via editor.construct.net/r135. I manually put that /r135 in.