I have an identical problem regarding "Embed Code" that's two-fold, but a stop-gap solution that works for both.
Background info: I edit my site using Chrome and am running Windows 10.
1st Problem: I drag and drop "Embed Code" onto a page. I can usually click into "Click to set custom HTML" the first time. Once I click out of the editing window, I am unable to get back into it.
2nd Problem: I cannot edit a second instance of "Embed Code" immediately after editing the first instance.
Dragging and dropping another instance of "Embed Code" onto the page does not fix either problem. I have also tried navigating to another page via the editor and then coming back to the page I'm working with no success of being able to edit the "Click to set custom HTML."
My current workaround for both problems is as follows:
(1) Hit refresh on the browser or F5.
(2) Navigate back to the page to be built.
(3) Click into "Click to set custom HTML."
This procedure will take you back to the home-page of your site, which is unpleasant news if you're working on a sub-page deep within your site. One nice thing about Weebly is that it auto-saves your work, so the "Click to set custom HTML" will be there waiting for you to edit.
This procedure is a pain is you end up doing it several (hundred) times, but it gets the job done. I hope this helps until a more permanant solution from Weebly's end can be realized.
