If I earn a bunch of my custom Advancements and then use the /mach reset <my username> command, at first it will appear to have worked, but the moment I earn any advancement, it will visually return to the exact state it was in before, showing all the advancements I earned before the reset. This happens 100% of the time, so recreating this for your development should be incredibly easy.
No errors, and happens regardless of configuration.
While trying to create the screenshots for this bug report, I couldn't actually get the advancements to visually reset at all. It appears that the only advancement it visually removed from me was the very first one (the wooden log). It persists between server reloads and it takes a full wipe of all advancement data and deletion of the generated datapack along with a full server restart to return the advancement screen to what it should be (if at all).