It's not like it sounds, but it's a problem for me. My realm experiencing a new trend of funny auctioning... everyone pusting auctions of single item per stack. F.e. 90 pages of Infinite Dust from 3-4 major sellers. No more than 10k dust overall. Trying to "Purchase All" more than 200-300 auctions through SearchUI (it's really FEW - only those undercutting below the set threshold) leading to disconnect. Queing them for purchase by one with open AH chokes on each key press. Closing AH does not make it significantly faster.
I got to workaround it using Snatch with set price, purchasing 100-200 items at each step.
It hangs before purchases start. When 500-600 items being queued for purchase. Even 50 items - "Purchase All" stutters notably. The more - the longer stutter, up to eventual disconnect.