Maybe you have also a layer of cache provided by the server.
You have already checked that you have eos-switch-theme.php, so this is ok.
Check also:
– In the backend refresh the page where you want a different theme, and check that the option is saved with the checkbox checked.
– If you have any cache on the server delete all the cache
– Check the same page adding a query argument to the URL, e.g. https://your-site.com/page-sample/ becomes https://your-site.com/page-sample/?example-argument=sdlkf
If adding a query argument to the URL as suggested in the last point works, it means the problem is related to some cache (the server, WP Fastest Cache, maybe a CDN, the device).