Does EXPORT also freeze?
Switch to Storyboard mode... 
Scroll the timeline. If there are very small black gaps, right-click each and CLOSE GAP.
In turn, try each of the suggestions in this thread. Though they may seem to be unrelated, they just might be.
If no joy, be aware that a number of issues can cause this. To track it down, let others take a look.
Share your project, either here or privately. The process is easy - just follow these steps closely...
Back up --- With your project on the timeline, click on MENU at the top-left. Click FILE|BACK UP PROJECT FILES TO FOLDER. Choose a folder and SELECT FOLDER.
Upload --- Use a free server - Google Drive, MS OneDrive, etc.* - to upload the saved, numbered FOLDER. Do NOT upload the individual VPJ or export file.
Get link --- Get a public link. If using Google Drive, right-click the file and click SHARE. If necessary change "restricted" to "anyone with the link can view"
Share --- Click COPY LINK | DONE. Paste that link here, or click the folder at the top-right of this forum to message it privately to me. It won't be shared.
* Before uploading, right-click the folder, click PROPERTIES. Look at the File Size to confirm that it's not too big for the free space on the server.