re: Pineapple guava tree

Well they are certainly rated for your area, surprising cold is killing off new growth in winter.

I’d suggest when the zoo re-opens you go over and find the curator over plants at the facility and pick his/hers brain for further info that might help you - those people are usually a wealth of knowledge. The plants are still young, so not bearing fruit is not surprising, but the winter dieback is puzzling to me unless you have cultivars that for some reason just aren’t adapting to your area.