That seems to be a known bug which was resolved in 2.8.3.
The OpenVPN AS release notes are available here:
https://openvpn.net/vpn-server-resources/release-notes/
The related entry I am finding for 2.8.3 in the release notes is:
"Resolved a bug where secondary LDAP server would not be called if first LDAP server timed out."
Can you try upgrading to 2.8.3 or higher?
As a side note, they switched the LDAP python module used in 2.8.0 which is a major change and seem to require ironing out of resulting issues. There are release note fixes related to LDAP all the way up to and including 2.8.4. Hence, it might be a good idea to use at least 2.8.4 to get the benefits of those additional fixes.
As of today, the latest version is 2.8.7 which was released on December 8, 2020.
You should be able to continue to use the same OpenVPN Connect clients already installed with 2.8.7 that worked with 2.8.2. Upgrading to the newer version of the clients that come bundled is recommended but is not a hard requirement.