I was listening to some songs in my lossless collection and I came across an album that sounded a bit muffled in comparison to the others from the same band. I ran Spek to check the files and surely enough, there seems to be a clear 16k filter of around -20dB in every song.

This is from a Japanese band called Demetori. Their work is really hard to find in the west, this specific album isn't even on sale in Japan anymore, so I had downloaded their discography in what seemed to be lossless rips. And for most other albums it looks perfect, so I just assumed this album was a fake lossless. So I looked around for any other rips of this album but every single one I found looks exactly like this one.

I went through some of their other albums and sure enough some of them sporadically look like they are filtered, others don't. And again, I tried looking around for other rips of the filtered albums but they all look exactly the same. All these albums even have their rip log files, and while they could be fake too, it's very unusual to see on a fake.

In short, I am wondering whether this filter is inherent to the recording of the album. Is it a known practice for bands or distributors to purposely reduce the quality of their CDs? Or perhaps could this be a mistake in recording? Would be strange considering most of their works look fine.
What do you guys think?