My currrent 'vanilla' (ie, no mods) version is 1.10.3 aa89, and this'll let me enable achievement for an ironman game, so I
suspect 1.10.3 aa89 is what you should be shooting for (unless there are different checksums on different OS - I'm on Windows).
Other than mods (which as Bunnytob well says are the main cause of checksum changes), changes to game files on your local machine can cause checksum changes. In steam, right click on your game in the menu and select properties from the pop-up menu that pops up, and then from that select 'Local Files', and then 'Verify Integrity of Local Files' and see if that does the trick. Good luck - let us know how you go
