This time, I don't think it was the SD card, but rather, the format of the Favourites Lists, due to the new version of Sentinel.
The new version of Sentinel changes the favourites list format, so when the SDS100 restarts to a default list, it initially can't read it, hence "nothing to scan". I found turning the lists off, and then turn what lists you want back on causes the scanner to re-read and reformat the lists in use without the parts of entries it doesn't yet understand. (Namely, the RID aliases, a new feature for the SDS150, but not yet in the other scanners supported by this version of Sentinel.)
Also, the screen layout looks a bit different........... I think the new Sentinel modifies the screen config file, too, to (attempt to) include this.