I have 4 lilac bushes. last year half of one died. this spring the other half never got leaves. I also noticed the bush next to it grew leave which have now shriveled up. this is happening to another lilac and another one never got leaves on half of it. attached are some pictures. if anyone has any advice I'd appreciate it.

I have read that lilacs dont like standing water and we've had a wet spring where their part of the yard was flooded for a few days more than once. but they've always been in this part of the yard and it usually floods this way.