Veeam B&R backup jobs failed to login to Qnap Nas after KB5011503 installed

Occasional Visitor

Good Morning, 
Veeam backup & Replication CE 11 (last release) installed on Windows Server 2019 Hyper-V VM from about 1 month
Veeam Backup jobs use as destination a shared folder on Qnap Nas.
Windows 2019 VM Italian language standalone, Qnap Nas under domain.
R&W user used for Qnap autentication it's local user for Qnap and Administrator for Win2019 VM.
All go fine before KB5011503 update
After this installation Veeam Backup job works only with guest user.
No other user can autenticate to Qnap with SMB 1, 2, 3
Error message on Qnap is 
"Processing MACHINENAME Error: Nome utente o password non corretta --tr:Error code: 0x0000052e Failed to process [isFileExists]. --tr:Client failed to process the command. Command: [isFileExists]. --tr:event:3:"

Trying to uninstal KB5011503 update, after reboot all veeam Backup Job returns to work.
Updating KB5011503 again all Job stop to work.
Could be this a bug?
Where I can report this to microsoft?
Thanks
Paolo

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