require-config raising TypeError: null is not an object (evaluating 'require.config')

At the end of the body section of my index.html I have the usual script tag:

<script data-main="require-config.js" src='./bower_components/requirejs/require.js'></script>

On web page reload I experience relatively often the "TypeError: null is not an object (evaluating 'require.config')" coming from the first line of my require-config.js file. The error seems to appear randomly. Sometimes I need to reload the page one more time to get the page running, sometimes more than 10 times. It looks to me as some kind of caching problem, but I have no idea how it could be fixed. I would appreciate your help.

I could reproduce this behaviour using latest Safari, Chrome and Firefox.