System information

• Steam client version: Nov 26 2018, at 20:15:48
• Distribution: Arch Linux 64 bit
• Opted into Steam client beta?: No
• Have you checked for system updates?: Yes

Please describe your issue in as much detail as possible:

I run Grand Theft Auto V through Steamplay.
After they pushed an update(I believe that was on December 11, 2018) it was downloaded by my client.
When the download was done I got stuck in a validation loop; Every time validation finished it started again after maybe 10 seconds.

I tried to make more space on the drive that contains the game as suggested by #5558 but it did not make a difference.

Filesystem      Size  Used Avail Use% Mounted on
/dev/sda5        96G   77G   14G  86% /          <- Contains Steam Install
/dev/sda1       834G  714G  121G  86% /media/win <- Contains the Library Folder with GTA V

/dev/sda1 uses NTFS through ntfs-3g if that makes any difference.

To see what would happen I clicked play and selected "Launch game as soon as it's ready"
which printed this error to the console:

GameAction [AppID 271590, ActionID 3] : LaunchApp failed with AppError_13 with "/media/win/steam_linux/steamapps/common/Grand Theft Auto V/update/x64/dlcpacks/mpchristmas2018/dlc.rpf"

This helped me fix the issue by copying the mentioned file from a friend (on Windows) who had already downloaded the update.