I'm now on the new Garmin Express update that no longer removes favourites, thankfully. And I've been able to put activities back into favourites on my Instinct 1 and Instinct 2 Solar, but on my FR 55 the bad Garmin Express update did something a bit different - it removed some favourites and put others in the regular non-favourite list. It put 'Run' into the non-favourites, but when I try to re-order 'Run' into favourites my FR 55 freezes every time, and has to be force restarted.
Boy has this been a truly awful time with Garmin Express, which apparently receives no testing before release.