Hello,
This is typically an issue due to site template forcing the width of an image at 100% like this (in your case, it's in responsive.css file, line 2) :
img {width: 100% !important;}
So, in your site template responsive.css file, remove there the " !important" for image width, to let Google Maps api able to work.
Note that using so many !important (a way to force a style for all html tags/classes) is not a good pratice, as it forces only things this way, with no flexibility for extensions AND external library (Google Maps for example) to specify some styling related to their own code and needs.
The !important is to be avoided as much as possible.
Good to contact your site template vendor so that they could fix this issue.
Hope this helps.
Best regards,
Cyril