Hi all, thank you for your comments. The issue has been resolved, after searching through different articles and bearing your suggestions in mind. I now use this process whenever I make changes to the report.
In Visual Studio
1. Clean the report project.
2. Build the report.
In AOT,
3. close the SSRS Report node, then right click Refresh
4. expand the SSRS Report node, then select your report name, right click Save.
5. If there is an error about the version in the server being newer, then right click Restore
6. Right click Deploy
I find that this works for my project.