Currently I'am working on a semi-large project and of course use save features to store information. The save feature basically saves the game whenever you beat a mission and it unlocks access to the next level. To make my life easier I have a global variable that is linked to a localstorage key. Both are linked to each sprite that represents my level selection menu.
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Now for the bug in Construct2 that randomly occurs. I put the code in to each sprite that if the global variable = a certain amount that sprite changes animation, plus its unlocked. For some odd reason Construct2 changes my global variable code randomly to another global variable, so when I run the game the next level is not unlocked. At 1st I thought it was me but now its happened right in front of my face. I save the game and the code changes right after I saved. 1st time I saw it I was like what the fack LOL.
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So if your save keys and variable somehow don't work, check over your code real quick before going nuts. It doesn't happen all the time but when making a large project it will start to happen, at least with me it does.