I have run into this issue many times. However, when it stops, I have no idea what happened. I can add text fine. I can change what the text says fine. It's when I start to change its symbology that the text and associated box disappear as if they never existed.
Any idea of what is happening?
I created a new project. Nothing special. When I am working on a map after I add a new graphic layer, I go to add text. When I add the text, as I type it comes up as I wanted. Once I have completed writing the text I then either click on the element properties to change the symbology or change them using the tab on the upper portion of the main window. It's what I do next that typically makes the text element disappear as if I never added it. The first time it happened to me, I was able to change the color of the text fine. It was when I went to add a halo to the text that it disappeared. I had already typed out text earlier in the day that I was able to symbolize as I needed. So, I just copied the text element, pasted it to the position I wanted, and changed what the text said.
The same thing happened on a different project a few months later. That was after I had worked on many other new and old projects using ArcGIS Pro. I resolved the issue the same way. I am once again having this issue.
However, it is happening when I go to change any portion of the symbology on the text. I have tried adding different text elements and it keeps recurring. I closed the project and reopened it, but nothing changed.