Same problem.. I wanted to test Stage 4 of 'Forgot My Lunch' which is in the arcade (so in the previous version it was working) but now I get this:
SyntaxError: syntax error
127.0.0.1/Platform_behavior.js, line 133 (col undefined)
This is either a bug in Construct 2 or a problem in a third party plugin or behavior - please report it to the developer!