Are you providing enough water?
Felix

Still seeing freeze die back here even though it has been months since the last cold snap .
Combine freeze stress , drought damage and hot , windy dry days - it's a wonder the plant is even alive !
Using a clean sharp pair of pruners , cut back to green wood .
Scrape the bark to find where the brown ends and green begins . Sometimes pruning will stimulate a plant to send out new growth .
Do not fertilize until the plant has recovered from so much environmental stress and regular rains return .

Thank you for the feedback.. I re-mulched (it had little mulch). I had sprinklers system but maybe they got not enough water. I will now prune them to see if it helps.

@fagopher, I'm seeing the same problem now on my pineapple guava. I live in central Texas and the plant took a hit in the Big Freeze in Feb 2021. However, new leaves popped up on new branches and everything seemed to be on the rebound until suddenly some leaves and branches started dying, while others seem fine. How did your pineapple guava fair? Did the plant recover or did the "disease" spread to the whole plant?