Connection Manager in SSIS 2017 Package NOT Saving the Password
By default SSIS saves and encrypts sensitive data (passwords, etc.) with something called UserKey. This means that no-one else is able to use the connection with saved password other than the person who previously saved the SSIS-package.

This can be changed through the SSIS package properties -> ProtectionLevel. You should select "EncryptAllWithPassword" and set a password to "PackagePassword" property and save the package. Now when you open the package next time, SSDT will ask you to enter the password. When entered, connection should be working just fine.