This type of issue generally occurs when you compose Campaign using Copy-Paste technique.
To resolve this issue, there are 2 solutions.
When you copy-paste any text in Drag and drop Editor, click this option on the top right corner as shown below.
Untick the checkbox Clean paste and wait for the editor to load again.
Now paste the text from the source and “Paste Formatting Options” will popup. You will see these two conditions:
1. If you select “Remove Formatting,” then only the basic structure of the text will be pasted, but the change will not work properly.
2. If you select “Keep Formatting,” then the same design will be pasted, but the change might not work properly.
When you paste using Ctrl+Shift+v (for Windows) and Cmd+Shift+v (for Mac), you will not get any formatting options. However, only text will appear. In this case, the change will work properly.