This article describes how to improve the speed of your SMB share with disabling the policy "Microsoft network server: Digitally sign communications (always)
creating backups takes unusual long
performance of the remote archive volumes are poor (only a few MiB/s)
remote share is a Microsoft Windows server
no performance problems by using "smbclient" on other Linux clients
Open the "Local Group Policy Editor" on your Windows server and goto "Windows Settings > Security Settings > Local Policies > Security Option". To improve the speed of your share you have to disable the policy "Microsoft network server: Digitally sing communications (always)". After changing the policy you should be able to read and write with normal speed again.