I assume the cluster which has bloomed 3 times has done so over a period of 3 years. Unless you like the look, dump it. Round Up damage is for 1 year only (maybe less on rebloomers?)

I've not heard of a pest spray that attacks plant genes. Garden Clinic aka Pests & Diseases may be of help.

There is the possibility of it being another iris. A bee pod volunteer at the original location? With mutant genes :-)

Yes for 3 years. I think it would have been a fungicide, or like treatment, rather than weed or bug killer. Each one is different even on the same stem, so guess I'll keep them as a conversation starter.
Thank You
Diana

Some people spray their iris regularly with fungicide for iris leaf spot without any distortion of bloom.

I've seen photos of very strange looking seedlings before they were tossed.