I am using a Siemens S7-1200 with VTScada and the Siemens TCP driver. Occasionally, certain tags will be modified fine in VTScada, but they are not written to the PLC program (although they should be). Other times they are changed correctly. It seems to be somewhat random. Would appreciate any advice anyone could give that might be causing this.
Thanks.

This could be due to many things from tag configuration to a communications issue. If you have SupportPlus with us, please reach out to our tech support folks for help with this. Otherwise, you may want to create some tests in your PLC and also implement feedback in your system so you can verify when written changes are not updating in your PLC.

If you have some more info you can post here on the configuration of some problematic tags etc, then we might be able to help out a bit more on this.