storage connected to the network: Synology DiskStation 500 GB transferred, 4 files damaged $ @ #?

I recently obtained a Synology NAS, I copied files, modified the copied files and at least four were corrupted (of ~ 500 GB). How can I find out what is defective?

I configured it with SHR-2 (two units can fail and can be recovered), btrfs (for repair and fault tolerance), ecryptfs (for encryption) in addition to that; Standard options for this NAS. I copied the files from a couple of my external drives to it, and then binary differed. I copied those files not through the network but with the external drive connected directly through USB and then copied via shell. The files were copied at different times (one group one day, one group another day). In each case of corruption, there are 24 contiguous bytes that are completely wrong (the original files are not corrupted). I ran the btrfs scrub command, which is supposed to be able to detect and repair some damage, found a problem and said it corrected it. But that did not solve any of the corrupt files. And making it more strange, but perhaps backed by the corruption detected by Btrfs, I'm pretty sure that the binary differed immediately after the copy and I found no problems, and only found these problems a week later.

I ran the Synology memory test twice, no problems were found. I executed a SMART extended control, all the "normal" units.

So, what the hell? Where did the corruption occur? Is it the RAM of the NAS? Is it a controller? Is it one of the discs? Is it btrfs? Is it ecryptfs? Other? I'm not sure if the nature of the corruption suggests something, it's intermittent and it has 24 contiguous bytes.

I'm a little scared. I'm not sure how to research, apart from trying to test each individual hardware part (at least RAM and disks). And, without finding a specific error, I'm not sure how I can trust my NAS with my files with this high error rate.

Thanks in advance.