So I was giving one of my friends OP on my sever, and a menu came up that said OP with cheats on/off, and I thought it wouldn't matter if I put OP with cheats on since I had them turned off, so I clicked OP with cheats on. This apparently turned on cheats for the server, disabling achievements. I'll admit, I changed the weather once, but that was it. Is it possible to get achievements back on my server?
If you have access to the server, you can disable cheating it by modifying world's level.dat and on the player in playerdata/*.dat with a nbt editor, but the missed achievements won't appear afterwards AFAIK.