I am also having problems with Google maps on my site. And, I did some tests on try.discourse.org and also got odd behavior there.
Some of the embedded links show up (usually ones that are just some random view in maps) and some don’t show up at all (usually custom Google map datasets). Let me put a couple here.
Here is a custom dataset someone was posting about here awhile back (Embedding custom created Google Maps)
This is just the URL, not the frame. It shows up when I recently posted it at try.discourse but the zoom controls don’t work. Same behavior here: picture shows up but no zooming. This is from an old post here at meta and the zooming is working on that old post with the same URL. Now the odd thing is on my site I put this exact same one in a Message and it worked there. So, there is something flakey going on for sure.
Here is an iframe I exported from Google of just some random view, not a custom map – it seems to work.
Here is the original iframe on my site that no longer works:
(yes there is probably nothing here because its broken).
Here is the raw link of the above iframe – it shows up but no +/- zooming is working: