Same value returning on node read (DB on siemens S7-1200) |OPC UA Standard|Forum|OPC Foundation

Dear,
Whenever I read a node, DB on siemens S7-1200, the same value is returned. If I disconnect and connect again, the value is updated and remains until I have the session active. Any suggestion ?

Reading implementation:

m_session.Read(null, 0, TimestampsToReturn.Both, nodesToRead, out resultsValues, out diagnosticInfos);