Annotations box remains stuck after adding an annotation

STEPS TO REPRODUCE:

1. Login with Admin or with an user
2. Go to a page, select some text (or a word)
3. Press CTRL + M and fill in some annotation text
4. Click "Add annotation" button
5. On the same page, select another text (or another word)
6. Press again CTRL + M and fill in some annotation text
7. Click "Add annotation" button

EXPECTED RESULTS

The first and respectively, the second annotations are added successfully.

ACTUAL RESULTS

After the first annotation is added successfully, when clicking "Add annotation" button to add the second annotation, its text box remains displayed (screenshots attached) and shows an endlessly spinning wheel until refresh of the page is performed.

Tested and reproduced on IE, Edge, Firefox and Chrome.