authentication problem after upgrade

[Curtis Vaughan]

Sorry if this is wrong group to write to, but not sure where else to go.
I upgraded our ubuntu postfix/dovecot mailserver from ubuntu 18.04 to 20.04 (keeping it on LTS).
Anyhow after upgrading I was getting authentication issues from dovecot. Specifically:

imap-login: Error: Failed to initialize SSL server context: Can't load DH parameters: error:1408518A:SSL routines:ssl3_ctx_ctrl:dh key too small

and

Warning: please set ssl_dh=</etc/dovecot/dh.pem

I tried various methods involving recreating the dh.pem (e.g., openssl dhparam 4096 > dh.pem) and putting the new file in /etc/dovecot/, but also in /usr/share/dovecot/, since the latter is what is pointed to by /etc/dovecot/conf.d/10-ssl.conf. (btw I changed it to /etc/dovecot/ )
Nonetheless, nothing resolved the issue.

Finally on one website I found a suggestion to remove ssl-parameters.dat from /var/lib/dovecot/
What I did was just rename it to ssl-parameters.dat.old
Now everything is working.

But should I be concerned is my question.

Thanks for any input!