I ran a PNG optimiser across the Moodle data to save some space (a few GBs). Unfortunately this was not such a good idea as the file hashes are used by Moodle for storing the file. It is actually working fine, but we are getting HTTP/1.1 206 Partial Content responses and slowness downloading the affected files. The file hash is used for the ETag and is stored in the database according to https://docs.moodle.org/dev/File_API_internals#File_API_internals which I would suspect is the slowness issue.
Is there any way to "rehash" files in Moodle, easily?
Otherwise I suspect I may need to take a look at our backups.