The reason is CurseForges' Launcher is missing the default Minecraft JAVA Arguments, without these will cause client lag such as judders or client lockups, commonly known as lag spikes. To fix CurseForge SevTech: Ages of the Sky lag, do this:
- Open the CurseForge app
- Click Cog > Minecraft
- Add this to Additional Arguments
- Increase the Allocated Memory to modpack authors recommended settings
- Click the top-right
- Restart the SevTech: Ages of the Sky, for no lag
Everyone who plays on your server will need to do this, share this page with your community.