Hi Thorsten,
Can you give an example of the sort of warnings you are seeing? A problem we are aware of – and are incrementally addressing with each maintenance release – is one of strict standard notices which are more prevalent with recent versions of the PHP runtime.
Often, setting WP_DEBUG to false (in your wp-config.php file) can address this – if it is already false then ensuring your hosting environment is configured such that errors are not displayed (which is any way a best practice in a live or production environment) is worth investigating – please reach out to your web hosting provider if you need guidance on that end.
Thanks!