Problem with SSL on Multisite

Hello

I am having troubles with SSL certification on my WordPress Multisite setup.

The problems with the SSL certificates started out of the blue this autumn. My sites were deemed “not secure” by all browsers.

And when I contacted the hosting company they added certificates and turned on “Lets Encrypt” and everything worked fine.

But then all their computers crashed, and after rebuilding their clients sites my sites were all insecure again.

I managed to get it working on the root web by adding and configuring the two plugins:

https://wordpress.org/plugins/really-simple-ssl/

and

https://wordpress.org/plugins/ssl-insecure-content-fixer/

this worked for the main site and now some of the subsites are OK too, but not all of them

My hosting company has come to the end of their knowledge on WPMU and told me that all their clients have abandond multisite!!!

Can YOU help me here?

Thank you very much