I think I've figured out what happened. For awhile recently, there was a feature that would let you select multiple sizes (one of the More . . . or Advanced features) at one time and incorporate that into a search. I did that, and saved it. Now when I use that search, the filter doesn't work, and also there are no mfgrs or sizes to choose from anymore. I liked that feature, but it appears to be broken! If I go back to a search starting from zero, then sizes and mfgrs reappear. Who is it here whose sig is "If it ain't broke, fix it until it is"? That should be eBay's motto.
The "in your face" commercial message that stands between you and your Summary page half the time when you login is truly annoying, too.