Perhaps there are some invalid characters present in the strings. This often happens when users copy-paste examples from HTML documents (e.g. webpages) and inadvertently copy newlines or non-breaking spaces or something similar. Or some "smart" character replacement is provided by your OS: those decimal points certainly look strange (but that might just the font you are using).
So, check the character codes yourself. Or save the variable STR in a MAT file and upload it here by clicking the paperclip button, and we can show you how to check the character codes. We cannot run screenshots, we need your data.
Also show us the complete output of this command:
which str2double -all
