Simultaneously submitting, one paper got rejected, other didn’t - what to do? There is a result R and teams T and U.

Team T submitted into a journal result R, but not on Arxiv. Team U then submitted result R to Arxiv, without knowing about the submission of Team T. Team U also submitted to a journal after publishing on Arxiv but got rejected. Now the paper of Team T is already published, but later than the Arxiv submission of Team U.

What should or can the Team U do?
Team U can genuinely claim the following in a future version of their article:
"After making our result publicly available on arXiv, we became aware of a similar result obtained in \cite{teamTresultPublishedPaper}."
Team U can congratulate team T and ask the following:
"Dear Team T, congratulation on your result R in journal J. As you may be aware, we have been working independently on a similar result as your recently published paper; our article was available on arXiv on Sept 2019. We were planning on acknowledging your independently obtained result in the next revision on our article, and we were wondering if you would agree to do the same." As pointed out in the comment, this is potentially obnoxious, and might not have any benefits.
Team U can submit to paper to the same journal that accepted team T's paper. "Dear Editor, we have noticed a recently published article by team T in your journal on result R. The same result was obtained independently by our team and made public on Sept 2019, a few months before team T's result was publicly available. We are wondering about the journal policy regarding publication of two papers that prove the same result, when the public record shows that the results were obtained independently and contemporaneously."
Alternatively, instead of asking the Editor on the possibility of such submissions, Team U may directly submit the article to the same journal with a cover letter asking to be considered. 
If members of team T were referees for the paper of Team U (the paper that was eventually rejected), this may constitute a conflict of interest. If a reviewer reviews a paper that proves the same result as an article written by the reviewer not yet public but currently under review, the reviewer should at least declare this as a conflict of interest during the review. Of course, reviewers are anonymous so there is no way for team U to know. Team U may contact the Editor that rejected the journal, saying     "Dear Editor, thanks for your consideration for our submission XXX that was rejected on $RejectDate. After the submission of our article to your journal, the same result was published and made public by Team U in OtherJournal. We are wondering if you could double check that no conflict of interest among the reviewers hindered the review process." this is potentially obnoxious, and might not have any benefits.


Beyond these, team U should try to have their result published. Team U can certainly claim the result in their CV, research statement etc. 

There are numerous cases of independently obtained results in hot fields and many papers actually include a sentence as in 1. above. When that happens, curious readers and historians can lookup arXiv or other public repositories (e.g. PhD thesis, etc) to check the actual timeline.