Pureline Pump Running Unexpectedly

I have a Pureline VFD pump (model PL2525) that’s been installed for a few years. I have it programmed to run at various speeds during the day. Recently I have noticed it running at a lower speed (1000rpm) at night, when the programming should not run it. I also noticed a snowflake icon lit on the control panel.  It has been colder recently, down to 45-55F.

I suspect the pump has a freeze prevention function, but cannot find description of such in the manual or online. Can someone confirm my suspicion or offer another possibility?