WinCC Client loosing connection for 4 seconds

Dear all,

in this project we have:

WinCC 7.5 SP2 + Upd 18. (before we had upd. 12 but we put upd. 18 because we thought this could maybe solve the issue but it didn't)

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2 redundant servers

8 clients.

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4 clients are on server 1

4 clients are on server 2.

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It happens that the clients lose connection to the server:

The screen shows for all objects the yellow triangle and on the alarm logging area is : lost connection to data server. From this looks like network issue but with Wireshark we couldn't find any package lost.

We try many things to find the route (network ping, wireshark, hardware, Wincc clients, change network cable from one client to other...) but nothing helped.

We found on : C:\Program Files (x86)\Common Files\Siemens\ace\bin\Diagnose

some files that are corresponding with the time that the connection lose happens.

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In the attachment is one part  of the document where is shown the messages from this time. Please if someone had this issues to help where and what could be the cause of this issue.

Thank you.

Best regards.

Edmilson8.

Hello Murof,

in the diagnose file  C:\Program Files (x86)\Common Files\Siemens\ace\bin\Diagnose

We found that every 15 min we have :

On the HMI on this time you can see a small small blink.

But the loosing connection happens when we have this message for both server on same time:
(example other client)