Here's an example from equivariant homotopy theory. Blumberg and Hill, studying multiplicative structures on equivariant spectra, defined a functor from the (homotopy) category of $N_\infty$-operads to the category of indexing systems, and conjectured that it's an equivalence of categories.

Three teams of researchers proved this conjecture at around the same time! Rubin posted his proof in May 2017, followed soon after by Bonventre and Pereira and Gutiérrez and White, who posted theirs on the same day in July. The latter two groups were aware of each other, and deliberately synchronized.

In this case, having three proofs is good: the proofs are different, and each proof has different advantages and disadvantages. Moreover, the papers do more than just resolve the conjecture; each has different additional material.