I don't know what it is either because I've been filing a large number of TTs as well. I can only think that it is because of the large amount of traffic the merchants are getting that things are getting lost. The oddest thing is this:

placed an order from Macy's on Day X
Placed a second order from Macy's on Day X+1
Macy's order #1 pends no problem.
Place a Third order from Macy's on Day X+5
Place a 4th order from Macy's on Day X+8
Macy's order #3 pends with no trouble. Nada on orders 2 & 4. Nothing was different with any of them. Cleared cookies, same browser, nothing running in the back. Definitely something on Macy's side.