Ok I got it, i had to specify ca file path for the connection string, now when I have done that i get the similar error just a little bit less expressive:
failed certificate just became connection error
No suitable servers found (serverSelectionTryOnce set): [connection error calling hello on 'xxx.yyy.mongodb.net:27017'] [connection error calling hello on 'xxx.yyy.mongodb.net:27017'] [connection error calling hello on 'xxx.yyy.mongodb.net:27017']
At least we know it resolves the names in the cluster and certificate must be fine now but I’m not really sure how to debug this connection error string