@limetech, bumping this thread your way again, we got your attention in November but lost you since then.
Issue is, anyone using Samsung SSDs (among other brands too) in a btrfs cache pool in unraid will see performance fall off a cliff due to partitions starting on sector 64. E.g., if you transfer a large file from/to the btrfs cache pool, all the dockers in unraid will lock up.
@wgards, best option for now is to drop your cache down to one drive and reformat to XFS.