cannot read from / mount Time Machine sparse bundle

Here's my problem:

I've lost data which should be on a Time Machine Backup. However, I do not succeed to restore it.

My TimeMachine Volume is a NAS. Writing backups to it has stopped to work for some time now, but the relevant data should have been written to it. The NAS still works fine for reading/writing, including TimeMachine Backups from other computers.

I can see the sparsebundle in the finder. When trying to mount it with Disk Image Mounter, I get an error. "Das angeschlossene Medium konnte von diesem Computer nicht gelesen werden" (not readable by this computer).

On the internet, I have found the recommendation to try "hdiutil attach -nomount -readwrite ...", which results in:

"/dev/disk2"

Then, the image becomes visible in disk utility. When clicking first aid, I'm immediately told that first aid was successful.

I still cannot access my backup files.

Then, I tried "fsck_hfs -drf /dev/disk2".

This is the response:

journal_replay(/dev/disk2) returned 22
** /dev/rdisk2
	Using cacheBlockSize=32K cacheTotalBlock=65536 cacheSize=2097152K.
   Executing fsck_hfs (version hfs-583.100.10).
	Block 2 is not an MDB or Volume Header 
	Block 7293694956 is not an MDB or Volume Header 
volumeType is 0
/dev/rdisk2 0000:  0000 0000 0000 0000 0000 0000 0000 0000       |................|
. . .
/dev/rdisk2 01f0:  0000 0000 0000 0000 0000 0000 0000 0000       |................|
	unknown volume type 
	primary MDB is at block 0 0x00 
	alternate MDB is at block 0 0x00 
	primary VHB is at block 0 0x00 
	alternate VHB is at block 0 0x00 
	sector size = 512 0x200 
	VolumeObject flags = 0x01 
	total sectors for volume = 7293694958 0x1b2bcf3ee 
	total sectors for embedded volume = 0 0x00 
	CheckForClean - unknown volume type 
	CheckHFS returned 6, fsmodified = 0

what does this mean?