We see scraped content all the time. Occasionally we see scraped HTML in full form but slightly edited.
In general I'd do the following:
- Disavow those domains in GSC. Also consider disavowing any domains pointing links at the mirror sites. It could be possible that they are building up junk links to a mirror site which canonicals your site. No idea why anyone would do that but worth covering your bases.
- Submit DMCA notices to Google, their webhost, etc.
- Take a look through server logs for anything screwy. If you see tons of weird traffic from countries that aren't relevant to your business, you might decide to block them with your .htaccess file.
- Certainly make sure nothing has been changed on your own site (canonicals, common Wordpress hacks, etc.), though nothing is suggesting to me that that has happened.
Other than that I would just keep an eye on it and keep an eye on Google Search Console.