Please post your crash log so we can better understand the issue that your game is having. You can find this if you:
open the FTB launcher,
Click on "My Modpacks",
Click the three dots on the top right when hovering over the Sky Factory 3 mod pack,
Click the orange Open Folder button on the right side,
Open the folder called "Crash-reports",
Open the latest crash text file; copy and paste all of the contents here:
https://paste.feed-the-beast.com/ then posting the link here on your post.
Finally, please provide us with information about what you're playing the mod pack on. Operating system, amount of RAM, CPU and GPU information.