It doesn't look like a sync error because exactly the same files to be deleted and copied succeed with one set of flags but fail with the other set ---
Succeeds (the one by @Ole):
--progress --stats=24h
Fails:
--stats-one-line --stats-log-level NOTICE --stats=24h
I didn't check the log because of the above but can if you tell me to.
Actually, the solution by @Ole works perfectly so it is on longer important to figure out why the above line fails. In fact, that also gives the time taken, which I was implementing in PowerShell separately!
Thank you a ton for your kind, prompt and continuous support.
My thanks to everyone here too.