There's probably a mistake in calculations. But your code is impossible to understand.. You have almost 500 events which probably could be optimized to 50 or less. You need to read about functions.
I suggest temporarily disabling those tweens and replacing them with simple "Text set Y". See if this fixes the issue with uneven spacing. If it does, the problem is likely with wrong timings - you are calculating the coordinates for new tweens based on previous tweens which have not finished yet. But this is just a theory.
Use Debug Mode - you will be able to pause the game and check everything. Console logging is also extremely useful when troubleshooting - add "Browser Log" actions to key events, you can print out information like object coordinates, variables etc. Press F12 in preview and check the log.