Hi,
For this issue, I have some suggestions as below:
1. Please check that whether the modified visual web part item has been added into the Feature of the current solution;
2. How about create a simple demo project for a test?
3. If the issue still exists, please create another project with a few controls in visual web part and do the test again.
Feel free to reply with the test result if the issue still exists.
Best regards
Patrick Liang
TechNet Community Support
