PCS-7 WINCC OS server - Redundant Named Connection Error:0X700C

Dear Team,

we are using PCS-7 V9.1 SP2, with two redundant servers and 15 nos. of clients.

We have upgraded PCS-7 V7.1 -> V8.1 -> V9.1 - all migration activities have been completed successfully in SEP-2024.

The plant has been running on a new system for the past one month - without any issue.

we have 5 nos. of S7400H PLCs, and they are configured via "Named Connection" in PCS-7.

Today one abnormal behaviour was observed, that one of named connection was stopped - (i.e. data is not shown in any of server for that specific connection). - rest of all remaining "named Connections" are connected and showing data on both servers.

for example, we can consider named connections are "PLC_1", "PLC_2", "PLC_3", "PLC_4" and "PLC-5" - in above case only "PLC_1" connection was stopped, rest of all PLC_2 to PLC_5 connections were ok. - no error reported in logs (that i am attaching at end of this topic)

i have check s7-connection diagnosis: where connection status seems normal and redundant.

Also check Channel Diagnosis: connection status also seems normal.

then we just stopped WINCC RUNTIME in server-1, - Still on Server-2 there is not data from "Named connection" “PLC_1”, then start server-1 RUNTIME again -this time data was ok in server-1, after server-1 started we have stopped Server-2, re-start wincc RUNTIME in server-2 – now data is ok on both servers since last 24 hours.

Below I am attaching log file for “SIMATIC_S7_Protocol_Suite_01”

Server-1 Logs for SIMATIC_S7_Protocol_Suite_01:

Server-2 Logs for SIMATIC_S7_Protocol_Suite_01:

what is error code: Connectionerror 1 "ESH_CON_S7_PRG" : 0X700C - i have not seen this code while i stop server.