Whenever I try to join a game, it says, "Could not join due to join script failure."

Solution 1:

This problem usually occurs when a bug in the script has been reached. It is the issue of the Developer, not you. I suggest you to open the dev console ingame (F9) and send a screenshot of it to the dev.

Are your friends VIPs? It could also be that you tried to follow your friend in a VIP server.

Solution 2:

So this happened to me before and I don't know if I can take any chances on doing this so but when this happens have you ever tried restarting your computer and then going back to Roblox or logging out of your account and logging back in to join the game you wanted to play? This happens to me a lot, so try that. If it doesn't work then I do not know what to do next so try that :)