Normal dieback or something more?

Last summer we bought a new house with quite a bit of established plants. They did great. This year most of them are having issues. Parts of the plants are dying off, sometimes growing for a while before dying, sometimes not. The main difference between this summer and last is the amount of rain we had in the spring and we've had a lab care company doing occasional fertilizing/herbicides.
I first noticed it with the late blooming white lilac bushes. Small parts of 3 bushes were dying and one was closer to half dead. I cut out the dead/dying parts and what's left is doing fine.
Then noticed it on my home run roses. Cut them way back and they seem to be doing fine now (but about half height).
Then saw it happening to our hedge. I'm not sure what type of plant the hedge is, but it's not an evergreen. It's 7+ feet tall and would easily grow another several feet if we didn't trim it. I've cut out some dead parts, but keep finding more.
Most recently I noticed that parts of my purple lilac bush are dying (now that it's done blooming). The leaves are wilting on random branches, and not recovering, sometimes dying.
Any idea what this could be? I'll try to get some pictures later today. If it's normal die back, I won't worry. If it's something else, I'd like to fix/prevent it. Especially on the roses and purple lilacs.

I had the curling and drying up of the lilac bushes too, and when I did some research it states that it's a problem with lilacs .Hubby and I cut them of and they are sending out new shoots and the bush is looking better now.Check and find out if the evergreens are Thuja because they tend to have drying brown leaves but they eventually go away . It's amazing that I deal with those same problems you are having now.I know roses get black ots on their leaves and then turn yellow and drop .i do not have that much trouble with roses. Hope I am of some help to you

No, there's no such thing as "normal die back" - there would be a reason for it, however obscure and even possibly undefinable. You should post pictures. Please look very carefully at the leaves including the undersides for insect infestation or signs of disease, and photograph those if any, and post.

Here's some pictures of the white lilac. First picture is two of the larger plants. The one on the left didn't have much dead. The one on the right had about half dead that I cut out. Second picture is a close up of a part that due that I haven't cut out yet. Third picture is something I just noticed in the end of some new growth. It's actually in several places. Last picture shows the flowers. There weren't many flowers this year but that could be due to my trimming last year (before I knew they were lilacs and how to trim lilacs).

Pictures of the purple lilac bush. First picture shows a large dead area. Second picture shows wilting. Third picture is a close up of dead branches.

Pictures of our unidentified hedge. First picture is the hedge from a distance (it's huge). Second and third show some dead spots. Last picture is a wilted/dead spot that I just found today.

We also have something killing of evergreen trees and messing with the crab apple tree. I've attached pictures.

When you say "killing the evergreens", what do you mean? Needle drop is a normal part of maturation for pines (that's a pine in your picture) and takes place along the trunk and at the base of branches. However, if you're talking about large sections turning brown and losing needles, it would not be normal.

White Lilac, pic 3: Looks like herbicide, MAYBE mineral deficiency.
Look along the branches where some twigs are OK and some are not. Look at the bark. Sort of like pic 2. Are there any sunken areas? Oozing sap? Holes? Small, perfectly round holes, perhaps 1/8" diameter?

Purple Lilac: Same investigation. Does not look like mineral deficiency.

Hedge (I think it is a Privet, Ligustrum). Other than the same questions as the lilacs, no idea. These 3 plants (Lilac and Privet) are close enough related to share many pests and diseases.
There are root diseases like Verticillium that attack many plants.

Evergreen Tree (it is a pine): Look for an insect called a Borer. There are many species that target different parts of the tree, but the types that attack the new growth are usually right there where you see the damage. Cut off a twig with the damage, including a bit farther back into the good wood. Investigate for damage, slowly taking apart the twig. Start by looking for holes or loose bark. Then remove the bark and see if there is damage under the bark.
Borers usually do something like this, though the exact details vary with the species: Female lays eggs, or may tunnel under the bark, then lay eggs. Eggs hatch. Larvae eat their way around the twig. Some go up and down, lengthwise. Others eat a path around the circumference. When they are big enough they tunnel/dig/chew their way out, almost always leaving a neat, round exit hole. They breed and start the cycle all over again.
This is also what I am asking you to look for with the Lilacs, when I suggest you look for small holes in the twigs or branches below the dead parts.

Crabapple: They get many of the same diseases as apples. Here is an example of just one such leaf spotting disease. There are many.
http://www.ipm.ucdavis.edu/PMG/GARDEN/PLANTS/DISEASES/entomoslfspt.html

Ask the company doing the maintenance what is going on. If they are applying fertilizer, herbicide, pesticide and other things, they ought to have someone on the staff to look into these things.

I'm about 99% certain we have line borers. We just have to figure out the best and most cost effective way to get rid of 4 huge pine trees. I want them gone. I'll look into the other stuff more this weekend. We're trying to get the lawn guys to come look at the stuff too. I'd be fine with not doing the herbicides since I'm still pulling most of the weeds (not sure the herbicides have been very effective). I'll look into what you think the hedge is and try to positively ID it (may post it on the plant ID forum).

Yes, the ID forum is the right place to ID the hedge.
Some close ups showing leaf attachment (several leaves on a twig), flowers or fruit, and some of the bark, especially on a younger twig. Most Ligustrum have specialized dots called lenticels, not many other shrubs have them.