Debug: SSL_get_servername() failed

[Rowan @ Jetboy]

I've setup Postfix to Dovecot LMTP delivery with mandatory TLS. Emails 
are being delivered with TLSv1.3 with no errors. However, setting:

verbose_ssl = yes
exposes this on each connection:

lmtp(405619): Debug: SSL_get_servername() failed

What it this mean, and what should I do about it?