Unity and AC: Syndicate far as I remember periodically have some sort of check or method of protection which will cause the game to shut down ("crash") if it detects certain changes to memory, I'm not all that great at explaining but that should be why it crashes although when I recently played through Syndicate it was fairly infrequent although getting the table to hook to the game was a bit of luck whether it would detect or not, could take a few tries and then some more tries to get it to properly detect the address for the player and enable the actual functions.
Fast-traveling, switching different zones and just playing the game for a period of time will periodically also update or reset this and it might be required to actually exit the game and re-initialize the hook to get it to update again, there's a key for updating the address in the table itself but I could never get it to work but I was probably doing it wrong or something, possibly.
Also I'm not sure how well the DLC is supported, I couldn't get the table to work at all with Jack the Ripper for Syndicate but from what I remember Dead Kings in Unity was functional although I haven't played that game in a while.
Ubisoft probably hasn't updated that game further, Syndicate got a small patch near the end of 2016 I believe but retained the 1.51 version number instead of 1.52 as it was called on consoles.
And the DLC is unstable on it's own, even without the CE table it just periodically crashes, seems to be a well reported problems at least but I doubt the game will be supported further.
Anyways hopefully this helps a bit on why the game does periodically seem to crash or well at least one type of crash the game has.
And I am pretty sure both Unity and Syndicate does use this little protection and has this thing about periodically updating the address for the player so it has to be re-checked for some of the functions to work as intended.
(Unless Unity actually retained the debug menu some of the earlier games had, that might work to bypass this anti-cheat thing.)
One of these days I'll replay the entire series, one day.
(There's only like thirteen games heh.)