JSON 502 error on -some- sites after server upgrade

I have a number of Updraft site licenses, and have been backing up each one to SFTP for a couple of years now. No problems at all. 10 days ago, I upgraded my server hardware (dedicated server at Dreamhost) which changed the address. Now I have this odd experience: at least one of the sites continues to backup just fine, but several others refuse, with the error “updraft_send_command: error: updraftplus: could not parse the JSON (502)”.

So, from that, I determine that it’s NOT a server-wide issue, else -all- sites would fail, not just some. I tried removing the license activation to one of the problem sites and then reactivating it. That did not work. I added in the MD5 key to the server. That did not work. I deleted the SFTP entry and created a new one. That did not work.

All of the backups are going to one main directory, and then to a given subdirectory. Therefore the login and password for all the sites is identical.

The JSON error pops up -immediately- (not after a delay.)

I have opened a ticket with Dreamhost, but given that some of the sites backup just fine, I suspect I’ll get back “check with Updraft; JSON is working fine here.”

Suggestions on how to reset everything and try over, and/or anything else that might allow me to continue using SFTP would be appreciated!