What your photo shows on the trunk is lichen and is totally harmless to the Ligustrum.

However, between several dying and one tipping over, I wonder if they were properly planted or if they had circling roots or were planted with the burlap still on or any one of a number of other possible planting issues.

Ligustrum are also extremely prone to honey fungus, Armillaria. And since this is primarily a root rot fungus, you may not see anything obvious until the trees start dying off.

You might want to take one of the plants (newly removed) with the roots intact to your local extension office for an accurate diagnosis.

Thanks so much nhbabs, but how would I know that? These plant are 4 years old. Why now? I am so concerned with losing more trees and also replacing the lost ones in fear of them dying too. I don't want to waste money. This is turning into an expensive situation.

Thanks so much Gardengal48. What is a local extension office?

Thanks again gardengal48, I agree with you. I started looking it up I am in Broward county in the state of Florida. The town of Fort Lauderdale

I thought of Armillaria also. Especially with what appears to be oak trees right there (in California there is a history of calling it oak root fungus).

Embothrium thanks! I am in Fort Lauderdale Florida

Here you go: Broward County Extension office.

I agree with GG48 that you would do well to try to get the issue IDed at your county extension service. If planting was the issue, it will be visible, with roots still in a relatively tight formation curling around, or the burlap still visible when you dig up the plant to take it in. However, both Embo and GG48 have more experience with diseases in areas with warm soil than I have, so their suggestion of fungus is definitely worth looking into since it is more likely to be accurate then my suggestion, which was just a general suggestion of issues that sometimes cause plants to fail.