Using the Prepare Form feature, I assume that you are working on the Acrobat DC application?
If you it is a windows computer, then you may try "Repair Installation" and see if that helps. Launch Acrobat>Help>Repair Installation.
If you are getting a similar error message shown in the help document Resolve Acrobat DC intermittent crashes on Windows then try the troubleshooting steps suggested.
For testing purpose you may check the same with different document, to see if its a document specific issue or application.