I don't really know. I've only had the OS 2 version, as my Playdate only arrived a week ago. So it had to have been some time ago. If the game was working fine before then, thin I'd disregard my comment. However you should contact playdate (panic) as this is apparently affecting several games at this time. Specifically ones on itch.io
Edit: by "this" I mean, where games in pulp were working fine and then suddenly they no longer can be added via the sideload option. I'm not really sure what the issue is but it is doing this for 5 other games that I had side loaded previously on day one. The files have not changed. So there's no reason they shouldn't be "able to resideload".