Since this DLL is part of the Ubisoft ecosystem, the file might be missing because your launcher is outdated or has a localized bug. Uninstall via the Control Panel.
This is the most frequent cause of the error. Many antivirus programs mistakenly flag uplay_r1_loader64.dll as a "false positive" and move it to quarantine, preventing the game from seeing it. Since this DLL is part of the Ubisoft
DLL errors are often side effects of missing system libraries that help the game communicate with your hardware. Since this DLL is part of the Ubisoft