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Plasma is only a desktop environment, and the Support > KDE Plasma forum category is for problems or questions specifically relating to Plasma.
Your problems appear of a different nature, which is why I’ve moved it to the generic Support category for now, although the presence of an Evil Nvidia™ graphics GPU in your system may warrant moving it to Support > Graphics & Display later. 
Interesting. The format of the messages you describe seems to hint at a kernel panic, but it could be something else altogether, including a hardware failure of some sorts — this includes overheating. 
The following paragraphs comprise a preformatted message with various links to things you should be looking for and ways to share information with us. At the very least, we’ll need an inxi output to know what hardware is in your system and what drivers are in use for them.
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How to Request Support
- How to post screenshots and links
- How to find error logs
- How to find system information
- How to post text information as preformatted text
- How to reach a minimal system
- How to use the terminal/
tty - How to use public Pastebin services
Tips and Tricks
Resources
Hint:
As a new member, you may want to subscribe to notifications for the Announcements > Stable Updates category. Every bundled update, whether it’s for Manjaro Testing or Manjaro Stable, always comes accompanied by a dedicated announcement thread.
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The first post of the thread contains the changes with regard to the previous bundled update.
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The second post of the thread details the potential problems, and how to deal with them.
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The announcement thread also always contains a poll (in the first post), and a summary of past issues (in the second post), for those who’ve skipped an update — which is not advised with a rolling-release distribution, but it does happen.
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Normally, it will either prompt you for a reboot or — at least, if I remember correctly — reboot the machine by itself when the backup or snapshot has been restored.
Depending on whether you have a rollback system with btrfs snapshots — which is the default on recent installations — or with actual rsync’d backups, the logs of the previous installation — provided that something did get logged, which of course does not happen if the kernel actually panicked — should still be accessible via journalctl. The links above should tell you how to retrieve that information.
It would surprise me if it did. That’s normally a pretty innocuous operation that shouldn’t interfere with the core system.
Which is good, but remember that you should then always store your backups on a separate drive, or perhaps on a NAS. Backups kept on the same drive as your system are not going to be of much help to you if that drive fails.