Version 20.12 sits at a crossroads. It supports many older modules (like the 1756-L61/L62 controllers) that newer firmware versions (v32+) have started to deprecate or limit. It serves as the last "modern" stop for aging hardware infrastructure.
A rapid-response security patch for the communication stack. It introduced "binary-incompatibility," meaning v20.03 software could only talk to v20.03 firmware. Opening a project in v20.03 permanently converts it, preventing older v20 versions from opening it.
Version 20 generally supports redundancy, but requires a separate, specific firmware revision for hardware in a redundant chassis. Rockwell Automation Operational Constraints & Known Anomalies Software Version Mismatch: