thanks a lot for your help so far! it already gave me some insight into what is going on.
within the server log from yesterday i see the following more specific reason why the writing of metadata is failing for this file:
2019-09-17 15:56:08: WARNING: HT: Error creating hardlink from “/backups/path/190917-0842/PATH/path.path/path/Path/Path/Path/Path/Pretty_long_Filename.pdf” to “/backups/path-path/190917-1531/PATH/path.path/path/Path/Path/Path/Path/Pretty_long_Filename.pdf”
2019-09-17 15:56:08: WARNING: File “/backups/path-path/190917-1531/.hashes//PATH/path.path/path/Path/Path/Path/Path/Pretty_long_Filename.pdf” has wrong size. Should=8 is=230. Error writing metadata to file. -1
2019-09-17 15:56:08: ERROR: Writing metadata to /backups/path-path/190917-1531/.hashes//PATH/path.path/path/Path/Path/Path/Path/Pretty_long_Filename.pdf failed
any ideas how to fix wrong size?
what is the best way to get a full backup “from scratch” - can we somehow ignore the problems of the past? 