I noticed that Construct 3 now uses stricter handling of variable comparisons against strings and numbers. For example, you can't set a text parameter with a number and have to concatenate it with a blank string or change it with the str() function.
Another case would be comparing dictionary key names with numbers, which can't be done anymore. So you have to change the integer into a string. This almost made me destroy the planet before I figured out what was going on, because my input bindings menu is heavily dependent on comparing key names with numbers.