privet question - ligustrum ovalifolium

Hi, Would be great to get some advice on this.  We have a long hedge made up of ligustrum ovalifolium. Probably around 8 years + old.  We lost one last year. All the leaves came off. Was hoping it would reflower this year. It did not, I replaced this year. This week I noticed the privet next to it started to loose it's leaves. Have read it could be two possible diseases. Popped into garden centre this week and guy told me it's probably just dehydrated and not a disease. There seems to be new growth at the very bottom, possible off shoot.. Have drip fed it water over a few hours and also put organic root builder powder in soil. Not sure what to do as do not want to loose the whole hedge!