I'm in the firmware bug camp too. Over/under on "the remote management server went down and a bug on all the freezers decided to put them back into some form of local control where its first action was to do a defrost cycle then put it back into offline service"?

Sure, that's possible?

It's also possible that, because the US is busy bombing Iran, Iran may be busy attacking the US infrastructure in any way possible? The US is also in a tepid war with russia, last I checked.

Some "cyber" crew getting a shell on an outsourced service provider and running a "defrost" command is also a totally explanation for this situation. It's also totally possible that some crew has mapped out a list of PLC entry points for various orgs and has them in a spreadsheet of "if we find a vulnerability, we should X this Y with this prestaged script that our intern / LMM cooked up last year to defrost these freezers"