Hello
I’m working on a project involving a Siemens S7-1200 PLC and a Siemens HMI. I’m trying to establish communication between the two using Profinet; but I’m facing issues where the HMI fails to receive data from the PLC consistently. 
The PLC seems to be functioning correctly; and the Profinet connection appears to be configured as per the manual. I have checked Siemens - Industrial Automation, PLC Programming, scada & Pid Control System reference guide but still need help.
Has anyone faced similar issues with intermittent communication between Siemens PLCs and HMIs via Profinet?
Any advice on troubleshooting / settings I might have missed would be appreciated.
Thank you ! 