What is your current CMS-version? Try to exit the admin panel and check example3.com again (in the latest version of the plugin, work was done on binding the theme to the backend-user for pages editing in CMS, most likely the reason is because if you are authorized as a backend-user, then the corresponding theme for backend-user is automatically attached). For what domain do you have backend users permissions? (although this should not affect, because restrictions for backend user only work in backend).
Try to reset the cache in the list of binds (sometimes it fails, if the record was edited).
Hard mode enabled?
I tested it on 461 build, did not reveal any deviations in the logic of work on the test server.
In general, judging by the given log, it should work correctly. Most likely, the error is somewhere at the cache level (This plugin, CMS, Web-server, Browser)
When setting theme2 as the default theme in mdomains settings, the correct theme is loaded. But the static pages content is not displayed in the page. The layout is displayed in the page.
Also, theme1 is loaded for example1.com and example2.com, and these work like a charm: loads content from static pages.
We suspect that example3.com never reaches your router: When enabling debug mode from the mdomain settings, example1.com and example2.com show the routing debug array. example3.com does not.
Also, the problem seems to occur with the ALL_THEME_PAGES_WITH_ROUTE_PATCH option: when creating a binding from example3.com/en/business to the business page, everything is fine, static page content of the business page is shown. But we do not want to create seperate bindings for all pages on our website.