Did you put any herbicide down on your lawn or nearby recently?  Any major changes in temperature since you planted them?  Do you know your pH for the soil?

No recent herbicide applications. We did have some big temperature fluctuations where I'm at, where our high went from 80 one day to 40 with rain and snow the next few days and now back in the 60s-70s. I have no idea what our soil pH is...Thank You!!

Because the new leaves are affected the most I suspect an environmental cause (ie the temperature change or herbicide issue) the plant will grow through either.  I do see some yellowing at the margins of the leaves.  When you see this type of pattern it is also environmental and can be from pH being off (lilacs like more neutral pH around 6.5) and/or can be caused by roots not absorbing nutrients in other ways if the soil was lacking certain nutrients or if they couldn't uptake the nutrients because of overly wet or dry soils.  You might be able to pick up a soil test kit from you Extension office below you might call ahead to make sure though:

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Salt Lake County
Government Center
2001 S State Street
Ste S1-300
Salt Lake City, UT 84190