That screenshot with the Body field shows that TinyMCE did not load correctly.
There are a couple of recent bugs and fixes on GitHub that related exactly to this.
You can start reading from here and then follow the links:
It works fine when composing the email from the lead overview page. The issue is with trying it from the lead detail page.
Do any of the provided fixes work for you?
Iām running 7.11.18, the latest version in a fresh install. The issue is present in Detail view but not in the overview. I can replicate the issue on the Softaculous demo,itās exactly the same there. I donāt understand the logic of starting to apply fixes in that scenario?
The fixes are so recent that they are only on Github, not included in any released version yet.
But since they are so easy to apply manually, by trying them you could get your problem solved, and it would help establish whether your problem is the same as that one (in which case you could close your Issue on GitHub as a duplicate).
Sometimes a video is worth a thousand wordsā¦
Yes, great vid, that is exactly what the problem is. Itās the same in Events. When you try to compose from Detail view, it doesnāt work. Basically, as soon as you DONāT see TinyMCE installed within the Body of the email, thereās no point in looking further, it wonāt work.
What I donāt understand is, you say you fixed it with some mods, but you just demonstrated that you still have the exact problem in your video. Or are you saying that it is only present on this (your demo) site and that you actually fixed it in another (your production?) site?
You didnāt watch the whole video LOL, I demonstrate the problem on my test install and then demonstrate it works on my production install. However Iāve just compared the two files involved in the fix and the fix seems to be already applied to the non-working install. So at least I can rule out thatās not exactly the problem.
The video stops on āI will check my code and postā¦ā then I get an eternal loading circleā¦ couldnāt see thereās more to comeā¦
1:37 I demo my production site that works. Iāve checked the āfixā and it is applied to both sites now, so thatās definitely not the problem. (at least anymore). Iām racking my brain to try and think of what else the problem could be. Theyāre both on the same server and the same version.
I stand corrected! My production is 7.11.15 and my test server (not working) is 7.11.18
Well no, thatās exactly my point, when you click from list view it works on my site too. Itās when you compose from detailed view that it doesnāt. Can you verify that on your production site?
At 01:59, when you go into the contact, can you not go down and instead click on the email address in the contact details, rather than clicking on the arrow and ācomposeā?
yes I also demonstrate that in the video (2:19). It works, watch for a few more seconds. I also just tried fix #8956
and that doesnāt fix it either.
Yes that absolutely works for me on my production.
Ok, gotcha. Thatās good news, at least you have the fix somewhere.
My production (thatās working) is on 7.11.15. On the issue in Github most people are rolling back to 7.11.15.
When you tried the fix, did you go through all those Repairs you recommended yourself? 
And this is the other fix:
Yep, I was hoping that would fix it, it didnāt.(the first fix, Iām trying 8913 now).