As of 2015 October 17, it seems you need to clear your browser cache after 20 or 30 maps. The problem has been reported for Firefox, Chrome and IE.
What happens when the cache fills up is that GMap just displays "Loading map" but never finishes.
Here are some notes on how to clear specific browsers: You can always look up specific instructions by googling "clear cache in Firefox". Also, when you clear the cache, there is a list of different things you can clear. Don't clear your cookies, all you need to clear is cached images and files.
I looked up "Clear cache in Firefox" and found instrucitons:
Just click "History", then "Clear Recent History", and "Cache"
Time Range: Everything
[ ] Browsing and download history
[ ] Cookies
- 15.11.14 Dan Richardson reports that he again had to clear his Chrome cache
(I looked up "Clearing cache in chrome" on Google: