From the upstream mailing list:
From: David Sterba @ 2021-09-21 19:56 UTC
The last function to fail is inside ZSTD implementation in kernel.
If btrfs passes wrong data to zstd we'd see that also on non-arm builds,
so guessing by mmiocpy as a copy-something function it could be some
sort of alignment problem that works on x86_64 but throws an exception
on arm as it's stricter about alignment.