syzygium lilly pilly superior lower leaf dropping

Alex24 starts with ...
I planted 50 syzygium (lilly pilly) superior in front of property about late july / early August in Brisbane.
Some of the plants ( not all of them) at the upper part of property (exposed to winds as there is no building / fence protection) started to drop their lower leaves and developing branch die backs . The upper part of plants seem quiet healthy and are developing new buds.

My initial guess was that these plants where exposed to cold winds we get in August. I have watered them regularly to maintain a moist soil and mulched the soil.
Either i was sold poor quality plants or these plants tend to lose leaves toward end of winter. or i am over watered them?

has any one experienced this with their lilly pillies?.

Pictures - Click to enlarge
Picture: 1	Picture: 2