SA-0013 when adding ESXi host

Hi folks.  I have two ESXi 6.5 hosts that my SAE 2.x has been monitoring for almost three years.  Back in August, SAE started complaining every week that it couldn't contact one of the hosts.  I checked a few things, but couldn't find a quick fix, so sort of forgot about it. 

Today, I decided to try again.  I forget what the actual error message was when I started today, but I figured - delete the device and the credentials and add it back in, and we'll be good.  The device and creds deleted with no issues. However, when trying to add the device back, I keep getting error SA-0013.  I couldn't find that one in the Support Assist 2 error code appendix.  Has anyone seen this before and know what the problem is? 

I've tried creating new creds several times, tried adding the host several times (by name and IP), even tried creating new creds while adding the host.  Nothing has worked so far.  The Windows machine running SAE can reach the ESXi host with no issues - I can login to the host WebGUI from the same browser that the SAE console is running in.  Also, the two ESXi hosts have different passwords and different creds in SAE.  I'm not using a Credentials profile, just simple credentials - I'm only monitoring the two hosts (VMWare and iDRAC), our Compellent, and a Windows file server VM.  Those other 5 "devices" are all connected fine, it's just this one ESXi host that's giving me problems.

Thanks for any pointers.

Dave