Just for reference, it seems to be that Discord’s game overlay prevents Roblox from catching keyboard input in some cases, as Relaix also mentioned:
Given the issue only occurs with Roblox, I still do think that Roblox has something going on that other games don’t, causing this issue. But for the rest of it, I only know of Discord that has game overlays for things like Roblox - and we don’t know what changed recently to cause this issue either 