The propagation of blocks in the Bitcoin network was hindered by a problem related to mutated blocks in previous versions of Bitcoin Core. A peer could send a mutated block to others, which would clear the download state of those peers that also announced the block, making it difficult for them to continue the propagation process. This issue was considered medium severity and affected features like compact block relay.
However, with the release of Bitcoin Core v25.0, this problem was fixed. The fix, #27608, ensured that a peer could only affect its own block download state and not that of other peers. As a result, block propagation was no longer hindered by mutated blocks. The fix was credited to Suhas Daftuar for noticing the problem and working on a solution. The timeline for this issue involved its first report in May 2023, the fix being merged in the same month, the release of v25.0 in May 2023, and public disclosure in October 2024.