We running 2 application on amazon ec2 (backend.abc.com & frontend.abc.com). For that application, we used a paid SSL Certificate. That
A permanent solution would be to reissue the SSL certificate from your provider and reinstall it on your server.
The reissued certificate would update the CA bundle.
Cheers!
If you're having this issue with "curl" (or similar) on a Ubuntu 16 system, here's how we fixed it:
On the Ubuntu 16 system hosting the curl / app that fails: