My server delivers the right cert when checking with chrome or the ssl-check-service you recommend. It also worked in previous versions of davdroid. With the new http lib it uses the default host cert and fails.
SNI stoped working after update
There is already a bugfix release 0.5.10.1 that fixes the sni issue. Wait some hours and you will receive the update automatically.
One must still have chaos in oneself to be able to give birth to a dancing star. – Friedrich Nietzsche