High Sierra 10.13.3 Update

1)

If you have kernel panic reports, can you please post 2 or 3 of the most recent? They may tell us something.

Kernel Panic reports: Finder -> Go -> Go to Folder -> /Library/Logs/DiagnosticReports

<http://support.apple.com/kb/ht2546>

<http://support.apple.com/en-us/HT200553>

The panic report should have "panic" in the file name.

2)

Please post the EtreCheck output as a "Reply" to this thread

<https://discussions.apple.com/docs/DOC-6174> or <https://etrecheck.com>

Use the EtreCheck -> Edit -> Copy Report (See the image below)

And then Paste the report as a "Reply" to this thread.

If, AND ONLY IF, you get the error:

"The message contains invalid characters"

then try posting to PasteBin.com, and give us a PasteBin URL link.

<http://pastebin.com/>

.

EtreCheck is a tool that helps Apple Support Community volunteers debug problems without any access to the troubled computers. Debugging problems can be a difficult task even when the machine is in front of you. Attempting it via a discussion forum is extremely difficult. EtreCheck is a great help that regards.

3)

You should also try an SMC reset and an NVRAM reset

<Reset the System Management Controller (SMC) on your Mac - Apple Support>

<How to reset NVRAM on your Mac - Apple Support>

Hi,

No ... for unexpected shutdowns in sleep mode, see if resetting the SMC helps > How to reset the System Management Controller (SMC) on your Mac - Apple Support

For more detailed information about this update, please visit: https://support.apple.com/kb/HT208375

For detailed information about the security content of this update, please visit: https://support.apple.com/kb/HT201222

Can you give more detail about the kinds of shutdowns you are seeing? Are they panics or is your system simply powering itself off?