WinCC V12 Professional Client-Server

We have installed on site for the customer, 1 WinCC V12 Professional Server and 2 Clients. The runtime project communicates with one 315-2 DP and currently has less than 200 tags. The system works for a while and then after some time all clients lose connection to the server (sometimes days, sometimes hours…recently it has happened every day). This is only fixed by restarting the server and clients. I have tried recompiling project from scratch and have updated to latest service pack.

The only clue I see in Windows Event logs is that Application Health Check in CCDmRtServer_Sync causes failover.

There is one tag EXP_GATE_PERC that logs complain about format, so that has been removed.

SIEMENS support has sugested that there is a malware-related fault in client, DHCP error on server and possible issue related to time sync between client and server.

Has anyone experienced this on TIA? Have searched, but only found threads for plain old WinCC V7.x

Thank you

Dhiren