When I mount the smb share with the same credentials on another pc, there's no problem.When I copy such a 'slow file' to the local drive of the users' pc, is always works as expected.The same files, which takes minutes to open from Explorer, open instantaneously when opened from Excel (recent files).The sluggishness only occurs the first time, the second time it works as expected and only when the files are opened from Explorer.When I move the affected file to another location on the same SMB share, the problem persists.I tested many files but it only affects some files, mostly Excel files.Users are working on either Windor 2004, fully up-to-date and using Office 365 Business. It affects user working on desktops who logon to the domain as well as local user who directly mount the SMB share. The problem started with one user and now it's multiple users who encounter the problem, however, I have not been able to replicate the problem on a test machine. The problem is that some Office files, located on an SMB share on a Windows 2019 Standard Server, open very slow (sometimes it takes as much as 5 minutes for 100kb file). So maybe there's someone who could help me? I am encountering this problem already for some weeks and I cannot seem to find the cause. I have been redirected here as they found it is likely a storage/server problem instead of an Office problem. The following question I raised before on the Office forums.

Slow microsoft office on mac