HMI KTP700 Basic communication problem with S7-1200

I began having trouble with HMI showing ###'s in fields that are to be read from PLC.  This appears to be a connectivity issue.  The diagnostic buffer of the PLC shows the following "System initiated session termination" "A previously established system session was terminated due to CPU operating system security efforts."

HMI = KTP700  with Firmware 17.00.00.06_02.01

PLC = S7-1200 1215 DCDCRly with Firmware V4.5.1

The HMI communication to the PLC was working until the HMI updated from FW 15.0 to 17.0

I am using TIA Portal V19.  I have the "Only allow secure PG/PC and HMI communication" UNchecked.  I have confirmed the date/time in the HMI matches the date/time in the PLC.

Does anyone have any tips for me to try to fix this?

Thank you in advance for your help.  I'm very grateful for this forum!!

Thank you for your help.  I had already installed V15.0 in the HMI and had a functioning connection.  After your suggestion for Compile>rebuild all I reinstalled V17.0 on the HMI but it functioned properly without performing a Rebuild All.  Maybe when you do a "Change Device" it automatically performs rebuild all?

The next time I run into this problem, I will remember to Compile>rebuild all to try to fix.

Thank you again.