OK, just so that I'm totally clear, you are presumably scanning photos into Tif format, and each day your scanning app starts over with the same file names, i.e. you created a file AA038.tif on Tuesday, and you created another file with the same name yesterday or today, is that correct? It's probably something to do with the fact that these are scans, but exactly what is unclear. With LR Classic, this theoretically couldn't happen as the matching criteria for duplicates detection is filename, capture date and file length. All three have to match.
It may be relevant, but what scanning software are you using?
Until we can get to the bottom of this, the obvious workaround would be to change the file names (e.g. add scan date if possible) so that duplicate filenames don't occur.