Me and my friend play on a server with skyfactory 3.0.6. Until two days ago everything was fine, but since yesterday we both 0 fps. It is not the fault of the server because even in singleplayer we have 0 fps
I've run into exactly the same issue starting when I got home from work last night. It was running fine when I went to work, my wife played on the server all night with no issues, and when I get home, I'm lucky if i can get 1 FPS. I tried everything. Uninstalled/reinstalled the client, system restore, driver updates and everything. It isn't the server cuz as op stated, happens in single player too. However, my wife doesn't have the issue at all and we run on the same network which is Fiber Optic. My computer is slightly better than hers and I regularly run at 60-100 FPS under the worst of conditions. I use the Curse/Twitch client as I can't seem to get it to download from the FTB client but I've played it from Curse since the beginning with no issue. Beginning to get really frustrated.
In Curse->Settings->Minecraft->Java Settings->Maximum Memory Allocation
Don't set it any higher than half of your physical memory, and generally no more than 8GB or 8128MB should be needed.
So if you have 8GB of physical memory then you shouldn't set it any higher than 4GB (4096MB).
Finally started happening to my wife today. After much trouble doing so, updating to 3.0.8 fixed the issue, however, our world wouldn't carry over so it kept crashing it, forcing us to have to rebuild in creative if we wanted to keep playing. So far, it's been the only fix I've been able to find with this. It's not a system issue or a network issue that I've been able to determine. We both have pretty beefy systems and both are in an IT related field. If upgrading versions doesn't help you, then I'm not sure what to do beyond that point. Just that it worked for both of us when we did it. Hope this helps.