sha1sum reports that checksums do not match even though they are identical

Perhaps I'm doing something very stupid here, but Google hasn't been very helpful in resolving the problem. I have an archive of files I made for backup purposes. I've generated an SHA1 checksum file from this archive: sha1sum myarchive.tar > myarchive.tar.sha1 The contents of this file are as follows: 6f5d7bdd71fe25ed8e881265fdb8a8bbcdaa41c1 myarchive.tar I have also run the SHA1 process in the terminal without piping to a file: sha1sum myarchive.tar This gives me the output: 6f5d7bdd71fe25ed8e881265fdb8a8bbcdaa41c1 myarchive.tar Clearly these checksums are the same. However, when I run the verification command, with the archive and its SHA1 file next to each other in the same directory: sha1sum -c myarchive.tar.sha1 I get an error message saying that the checksum does not match: myarchive.tar: FAILED sha1sum: WARNING: 1 computed checksum did NOT match Obviously something is wrong here, but I have no idea what it could be. Can anyone enlighten me? EDIT: Interestingly, doing two consecutive MD5s on the file comes up with two different checksums. Now I'm very confused. $ md5sum myarchive.tar 9a15036eed341613bbcf2c4b53a09859 myarchive.tar $ md5sum myarchive.tar a662d6b469627c62f2b03ee0df067436 myarchive.tar EDIT2: Additional context: * This is on real hardware (my Ubuntu MATE 19.10 desktop machine). * The archive I've made was destined for a Blu Ray backup disc. It's 22.6GB in size. * Performing an SHA1 verification of the file as burned to the Blu Ray disc ends up being successful. EDIT3: In response to requests to see the output of dmesg, there appear to be a few errors like the following: [ 7102.039819] perf: interrupt took too long (2502 > 2500), lowering kernel.perf_event_max_sample_rate to 79750 [ 8278.017874] sr 4:0:0:0: [sr0] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE [ 8278.017876] sr 4:0:0:0: [sr0] tag#0 Sense Key : Blank Check [current] [ 8278.017877] sr 4:0:0:0: [sr0] tag#0 Add. Sense: No additional sense information [ 8278.017878] sr 4:0:0:0: [sr0] tag#0 CDB: Read(10) 28 00 00 00 00 00 00 00 01 00 [ 8278.017879] blk_update_request: critical target error, dev sr0, sector 0 op 0x0:(READ) flags 0x80700 phys_seg 1 prio class 0 [ 8278.019391] sr 4:0:0:0: [sr0] tag#0 FAILED Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE [ 8278.019392] sr 4:0:0:0: [sr0] tag#0 Sense Key : Blank Check [current] [ 8278.019392] sr 4:0:0:0: [sr0] tag#0 Add. Sense: No additional sense information [ 8278.019393] sr 4:0:0:0: [sr0] tag#0 CDB: Read(10) 28 00 00 00 00 00 00 00 01 00 [ 8278.019394] blk_update_request: critical target error, dev sr0, sector 0 op 0x0:(READ) flags 0x0 phys_seg 1 prio class 0 [ 8278.019396] Buffer I/O error on dev sr0, logical block 0, async page read I think this is to do with my USB Blu Ray drive, though someone may be able to correct me.