This is a bug report of a system affected by https://github.com/openzfs/zfs/issues/6224
I do not remember how or when I triggered this bug since I noticed the problem when it was already too late. Given the extent of the corruption of my pool, I speculate this happened when I moved from pushing replication from my 11.2-running source system to this 11.3-running target, to pulling the other way around (as I was keen on benefitting from the implementation of resume transfers, a.k.a "send -t" which is natively supported in 11.3).
As stated in the forum, that's the maximum extent of the information I'm able to provide. Attached is the source and target debug information, although this bug was probably initially triggered many months ago.