As I said in my previous message all but the last two items have disappeared from the bottom row, can you see that on the top pair of images (bottom row) there are very many items to the left of the last two items, all of those are missing from the bottom image.
I will try the two line approach but for me that is a very poor solution (if it is one) because I don't want the taskbar taking up that much room. I have always preferred it hidden but I could tolerate one row visible all the time but not two.
The reason I ask is there is a possibility your rows have gone to three and you are only seeing two. Making two (or three) rows show should let us find out if the problem is a painting one or if the items are in fact missing.