Not all engines are capable of reading the Syzygy format. It's the new kid on the block and an older engine, or an engine that hasn't been coded to use it, won't be able to. If so, you would have to choose Syzygy (GUI). If you do, the GUI will check the tablebase and report the result.
Houdini 4 and Stockfish and Deep Fritz 14 are all capable of reading Syzygy. If so, you probably want to choose Syzygy (Engine.) If you do, the GUI WON'T read the file, but will leave it up to the engine to do so.
If you set up a position in the tablebase, and if have Syzygy (Engine) option chosen and the engine continues to calculate that position, then it doesn't sound like it's reading the file properly. As you pointed out, it should instantly reference the file and report the best move.
Hey guys, quick question: how does one load Syzygy tablebases into Chessbase 12 or Deep Fritz 14? I have a folder with the 3-4-5 men tablebases and when I go to Options -> Tablebases I find that there are two options: Syzygy (Engine) and Syzygy (GUI). What are the differences between these? Also, while it seems like I was able to get Stockfish to use them, it continues to calculate. Would it not instantly be able to reference said tablebases and give an exact continuation?
Thanks!