The most obvious issue is when numbers in JSON are not parsed correctly by JSON.parse in browsers and you have to use a custom parser or keep numbers as strings

The most obvious issue is when numbers in JSON are not parsed correctly by JSON.parse in browsers and you have to use a custom parser or keep numbers as strings, see this SO question https://stackoverflow.com/q/18755125/333777 https://stackoverflow.com/q/18755125/333777. I've encountered this several times when big numbers were serialized in Java, the Swagger said it's just a number and nothing about possible size limit and you eventually faced the issue in one of the bug reports when stuff broke.