Error while creating email using HTML

When I’m choosing to create email using HTML, there is an error where in ‘advanced’, I’m unable to see the HTML input section (this is not the issue, you can just type a text in the give text box, and save once, and then again go to advanced tab, and you’ll find the HTML input section)

Now the problem is, when I’m entering the code and then saving it, it shows an error which says “Your request could not be processed, please try again”, and then I reload it and again, enter everything only to see it again.

Now, I’ve been observing this for quite some time. It solves automatically after some time. Suppose I’ll do it today, it won’t get saved, but the next day, it will save without showing any error, but whenever I try to create a new email, this shows every time.

If I want to create an email today, I can’t do it.

If any of you have any solution for the same, please help me out.