PLC buffer keeps returning "System initiated session termination". I understand this is an issue with certificates, but I am using default/ auto-renew certificates.

Enabling Secure Mode on the HMI made this error go away, however, this doesn't make sense as legacy communication is allowed on my PLC. Why did this work? I want to know if I actually fixed it.

PLC: 1214C DC/DC/DC FW 4.6 (Downgraded from 4.7)

HMI: TP900 FW 17.0.0.8 (Upgraded from 17.0.0.0)

Other things I did to make the problem go away but didnt work:

- Set all modules to sync time with PLC (no RTC server)

- Factory reset both HMI and PLC