Debugging WebAssembly in a web browser is still pretty crude. For example, at the time of writing, it is still not possible to directly watch a variable using the debugger. In both Firefox and Chrome, you must occasionally refresh your browser to see the CPP source file. Unlike debugging JavaScript, the WebAssembly debuggers feel (ironically) buggy. In Chrome, you frequently have to click the step over button several times to advance the line of code. In both browsers, breakpoints sometimes fail to work.
I frequently have to remove and then re-add a break point to get them to work again. It is still early days for WebAssembly source maps and in-browser debugging, so the hope is that the situation will improve soon. Until it does, try combining debugging in the browser with the addition debug statements, as I advised earlier.
