Similar problem. The PLC is CPU 1517F-S PN/DP,  HMI is KTP900 Mobile.  What I did:

1. Running PLC simulation and RunTime:

- change PC/PG interface settings for STEP7 and for WinCC to all PLCSIM points ( local, TCPIP, Profibus, ISO ... )

- HMI introduced to PLC project and configured connection to local ProfiNet

2. Running PLC simulation and HMI simulation

- the same as above;

- changed HMI device to the panel with Profibus and connected the HMI to PLC ProfiBus.

- configured connection via Profibus, CPU master address2, HMI slave address 1

The best result is online diagnostic says that the HMI is not accessible or reachable.  Didn't appeared in available nodes list.

The confguration works on hardware: no HMI device in PLC project.  Connected via ProfiNet. HMI communication settings a single connection via S7Online on ProfiNet.

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Split from HMI Simulation not going online.