B. Edmun

I checked the Current Blocks and filtered for the known IP addresses of our admins.  These addresses are not in the block list. The Live Traffic view, filtered by Registered Users, shows error type as Failed Login. The first failed attempt shows up as Human, but any subsequent attempts if done in quick succession show up as Bot. 

One of the IPs used by the server does have a block for a bot hitting https://thebeergearstore.com/wp-cron.php?doing_wp_cron

I unblocked the IP, and the Diagnostic report no longer shows the Connectivity error in red that you pointed out. Yet, I still get a login error, “The username or password is incorrect,” even though we have not recently changed passwords.  So I went into the WP database via phpMyAdmin and cleared the passwords, reset the user_pass field with our existing passwords, then saved it as MD5. This is what finally worked.

Thank you for your assistance. I hope this thread helps someone else in the future.

I did attempt the full conflict testing method and cloned the entire site to a sandbox, switched to Twenty Fifteen Theme and turned off ALL plugins except Ultimate Member – The problem still persists.
Users are not allowed to log in a second time.