I tried smbv1 and also smbv2 but that didn’t solve the issue.
To solve the problem I created ~/.kodi/.smb/user.conf:
[global]
lock directory = /home/osmc/.kodi/.smb/
client max protocol = SMB2
name resolve order = bcast host
client use spnego = no
client ntlmv2 auth = no
Then I restarted the Pi and now it is working. Thank you for your help!