Ensure that your Lambda function has the necessary role attached to it, to be allow it connect to the RDS instance located in your VPC .
Also make sure that the client's certificate matches the database instances certificate, in your case the rds-ca-2019 is being used with the lambda, the RDS instance should also make user of this certificate. If your instance was launched after 14 January 2020 it would already have the latest certitifcate 
Hope this is of some help
Thank you for your reply. Unfortunately those are not the issues as I can connect just fine without SSL and the database is updated to use the new certificate. As mentioned I connect with that certificate just fine through MySQL WorkBench.
I am experiencing the same issue, did you get it resolved?
The MySQL version was too old, needed to upgrade (I upgraded to 8)
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