Basically, when I add some nodes in the provider side, these nodes are
replicated to the consumer side, but when I delete some nodes in the
provider side, the consumer side remain untouched. This confuse me.
For quite a while, this confused me too. It turns out there were some
syncrepl bugs, tracked down by this point. Are you running 2.3.27?
Upgrade if not, and observe closely. Turn on "sync" loglevel.