Open (older) Email with Attachment, Name for Attachment is "Untitled" and Click on this mean "Attachments can not be downloaded"

[mw]

System: Migrate from Zarafa 7.1.11 to Kopano.

Open Email (create in Zarafa) with Attachment, Webapp say Attachment Name is ‘Untitled’. When i click on this “untitled” Attachment, WebApp mean “Attachments can not be downloaded”

When i forward this email and click “send”, i see a warning:

“The attached files are not uploaded yet.
Do you want to send this message without attachments?”

I Click to “Don’t Send” and wait some time.
Now i see the correct Filename for Attachment.
Then Click “send” and the email will be sending.
The recipient see the correct Attachment.
This Problem is not by all “old” Email, but by many of it.

The Old-System (not more active) have no problem with the same Emails.

I don’t found Messages in Serverlog (Debug-Level).

Have some one any ideas?

Graeting Maik