I was looking for the same issue, I though that it’s only me how is having this strange and frustrating problem, I really understand how frustrated you are, as I had to retype or re copy the same text again and again to see when the text stop when i hit save to know which character is wrong and have to change it, the same characters you reported trigger the same issue for me. I have 3 blogs which almost the same setup and same plugins and the other two sites work the same, the only difference between the one that is working and the one that is not working is the BulletProof Security has created a htaccess Core and here I think the problem could be.
I am not a wordpress technically professional in coding so I would really appreciate if someone can tell what do I need to check or update in the htaccess file.
Please help as this is really time consuming task to keep editing the text tell it save the full post.