Excel 2016 hangs opening network files

Have a DELL Precision 7710 running Windows 10 Pro x64 v1709, Office 2016 Professional x32, SOPHOS Central Endpoint, and BitLocker Encryption. Excel 2016 Professional hangs for roughly 3 minutes when opening a network file with links to other worksheets. Sometimes, it appears to be related to exiting protected view, via "Enable Editing". The problem is frequent, but it does not seem to happen 5-10% of the time. When the file opens correctly it takes about 15-30 seconds. System is up to date (Windows and Office) except for KB4088776 (which won't install). Other types of laptops (Latitude 5480) are exhibiting the same behavior (laptops are both docked and not docked). Here is a list of what I have tried.

Disabled SOPHOS

Remove Realtek Audio Software (& disabled the Waves Audio Services) per DELL issue ( www.brucebnews.com/2017/07/a-possible-fix-for-the-excel-slow-file-opening-bug/ )

Excel Options->Advanced->Display->Checked "Disable HW acceleration"
Excel Options->Advanced->General->Unchecked "Ignore other applications that use DDE"

Detect & Repair Office (Basic)

Changed default printer to Microsoft PDF

Added network share as a trusted network location to Excel (in registry at HKCU\Software\Microsoft\Office\16.0\Excel\Security\Trusted Locations) (specifying both UNC & Drive Map as locations)
Deleted Registry key HKCU\Software\Microsoft\Office\16.0\Excel\

Tried a new LOCAL profile
Tried another never been used Latitude without Bitlocker Encryption

Turned off Intel speed step (BIOS)
Disabled Cortana (as in killed running executable, and renamed the Windows\SystemApps\Microsoft.Windows.Cortana* folder)

Thanks in advance!
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William FulksSystems Analyst & WebmasterCommented:
This has been a problem with Excel for as long as I can remember. You've done pretty much everything I'd recommend doing, so I wonder if this may be partially a network issue. Have you tried doing a file copy from the server to your PC just to see how fast it goes. If you're linking to external files that are kind of big, that may cause some issues. Are any of those files running macros?

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bitxpertAuthor Commented:
Thanks for the replies. We are not using DFS, and the server is actually an IBM midrange (iSeries). The spreadsheets have many links, but no macros. William, you are correct it was a network issue, and I resolved it by enabling SMB v2 on the iSeries.
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