Unrecoverable error

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Perhaps if you contain more information in your Q: then there may be something

to work with here. ~An example of an "unrecoverable error" -- could mean Kernel

Panic; or system damaged by some other process, as it stands without diagnostics.

Or a partial message, that we'd need to see, read and research to decipher if possible;

if there's more to message (has to be) ~ please include context and missing words.

• Don't Panic! Troubleshooting Kernel Panics in macOS

https://blog.macsales.com/39112-rocket-yard-guide-understanding-troubleshooting-kernel-panics

Were there 'Kernel Panic' messages in restart windows?

Or are there any 'VM Software' in use in your Mac?

These error messages are Symptoms of the underlying issue.

Or may (among others) be something like this situation:

• Mac Installation Errors You Encounter and How to Fix Them

https://blog.macsales.com/45723-mac-installation-errors-you-may-encounter-and-how-to-fix-them

Also there are Mac system logs with massive amounts of hidden details; most these

do more to confuse, instead of enlighten. However this evidence may not be invisible.

Incomplete questions have little else to offer ~ except wonder what else was involved.