Trouble running rdiff-backup after Windows updates

We have used rdiff-backup for well over 10 years for our Linux servers 
and workstations, and until recently to back up Windows servers and 
workstations we mounted their drives locally on the backup server and 
ran rdiff-backup against the mount. When our first Windows 10 
workstations arrived with v1909, we started having trouble reliably 
mounting the drives, so we recently put the Windows executable of 2.0.5 
on our Windows workstations and tried the same method we use for Linux - 
a cron job on the backup server would ssh to the Windows workstation 
(running the built-in OpenSSH server) and call a batch file that would 
run rdiff-backup, sending the backup back to the server. Keys were in 
place to allow passwordless connections. This way we could schedule 
several workstations to run in sequence without having multiples overlap 
in time (as might happen if we did the scheduling at the workstation). 
That was very stable on workstations running Windows 10 1909 and below. 
Then we upgraded all of our workstations to 21H1. Now we can manually 
ssh to the Windows workstation and run the batch file and it runs just 
fine. But if we run the cron job script that does the ssh and runs the 
batch file, everything works (setting environment variables and updating 
specific local files from network masters using scp) until the 
rdiff-backup command. We don't have "echo off" on the batch file so we 
can see the command issued. It makes the connection to the backup server 
and starts rdiff-backup on it, but then it hangs and doesn't progress 
any further, and no files are updated in the backup destination. We 
started with rdiff-backup 2.05 using SysNative in the remote-schema, 
then moved to 2.1.0a1-64 to see if that helped (changing the 
remote-schema to System32 but leaving everything else the same). but 
nothing changed except for an added warning about the server not 
understanding the API. If we are running the cron script in a terminal 
we can press Ctrl-C and exit. If it runs from a cron schedule we have to 
kill rdiff-backup on either the workstation or the server. Has anyone 
else seen something similar?

The command in the cron job is: ssh ${BACKUP_USER}@${TARGETHOST} 
rdiff-backup.bat ${BACKUPTO}; RDIFF_RESULT=$?

The command in the batch file is: 
C:\rdiff-backup-2.1.0a1-64\rdiff-backup.exe -v 6 
--exclude-symbolic-links --remote-schema 
"C:\Windows\System32\OpenSSH\ssh.exe %%s rdiff-backup --server" 
--include "C:/FuturaData" --include "C:/Program Files (x86)/Futura 
Systems/FuturaGIS/Staking Client" --exclude 
"C:/Users/%BACKUP_USER%/AppData/Local/Temp" --exclude 
"C:/Users/%BACKUP_USER%/AppData/Local/ESRI/Local Caches" --include 
"C:/Users/%BACKUP_USER%" --exclude "C:/**" C:/ 
[email protected]::%BACKUPTO%

Both use environment variables set on the command line of the script or 
earlier in the script.
-- 
Michael Crider, IT Supervisor
Howell-Oregon Electric Cooperative
West Plains MO
http://www.hoecoop.org