hi :)
this error happens when the chapters are not being combined in the right way. you should combine them from the start- merge chapter2 into chapter1, open the game and see in the lower right corner of the main menu that the game version is 2.09, then merge chapter3 into them in the same way. after starting the game again you should see that it is now version 3.57.
you should also join the discord server to ask there in case that you still have problems or need help with the game, answers there are faster.