I had the exact same problem.
I saw a post by chris and got work reconstructing my DDY file with the ASHRAE clearsky model which is sufficient for my needs. I also realized that using the LB EPW to DDY the results are just 2 design days (winter and summer, the DDY had multiple months of design days) and also with clearsky. With this, the results are very similar between the HB to OSM and Peak Loads!
Maybe try to unify the sky model using chris’s post that I mentioned along my screenshot.
