Modpack version
1.70b

Issue
I tried to update the game for a while now first to 1.70C now to 1.71 and it fails it said the files are being used by another application please exit etc, now I tried to update this after a full PC restart, after PC has been left off for a day and after i exit trumpetear or eartrumpet or what i saw online people say exited steam, did all the exiting i could when it comes to apps, still can't update, but i can update other modpacks.

Logs
N/A

PS: Did alot of troubleshooting and searching on google for the past week if not more.

I had the same problem. I ended up having to install a new instance and transfer my save and journeymap folders.

That is indeed the way to fix it. It's a Twitch issue I'm afraid.

Not to reopen, but to leave a remark. The modpack is installed with a "read-only" flag on the folder. If you go to the modpack folder, right-click, select properties and uncheck the "Read-only" flag, you can upgrade your modpack again. Not sure if that's Twitch or how the files are being distributed - anyway, with this method you don't need to copy your safes around. But you do need to do it after each update.
The "read-only" flag is responsible for the "files are in use" message that you posted.

Twitch is responsible for that, but very nice to know, thanks.