The latest patch file may have failed to save.
It should be saved in "Documents/My Games/Warlander/Steam/user_id/download".
Check to see if the Warlander directory exists in the Documents folder.
If it exists, delete it and see if this fixes the issue.
If it does not exist, the "Windows Defender ransomware prevention" function may be ON.
Refer to the website below to allow Warlander to make changes to Documents.
https://www.gigafree.net/Windows/Controlled-Folder-Access/
(Japanese website)
If the problem persists, try changing the location of the Warlander folder.