If a Web Part was incorrectly deleted from the page, it will not be completely removed. The Web Part could still have some resources running on the page that might increase the page loading time.
Find out if there are any hidden Web Part on the page utilizing the Web Part Maintenance mode from SharePoint.
Step 1. Check the number of Web Parts on the page
Edit the page. Count the total number of Web Parts that the page has.
For example, the following page in edit mode shows only two Web Parts (Events & Documents):
Step 2. Open Web Part Maintenance mode
Add ?Contents=1 to the URL of the page and hit Enter to open the page in Web Part Maintenance Mode,:
Step 3. Detect Hidden Web Parts
Once the Web Part Page Maintenance Mode is opened, it will show you a list of all Web Parts running on the page, including those that you do not see (Hidden Web Parts).
Our sample page, that only has two Web Parts in edit mode, in the Web Part Page Maintenance mode has a total of 3 Web Parts (2 Documents and 1 Events). It means, we have 1 extra Documents Web Part that is hidden:
Step 4: Delete Hidden Web Parts
Now delete the Hidden Web Parts.
In our example, we see two Documents Web Parts, but we do not know which one is the hidden Web Part that need to be removed, and which one is the real Web Part that is rendered on our page. That is why we will select them both, and click the Delete link.
Then we navigate back to our page, by clicking the Go Back to Web Part Page option, to add the Documents Web Part back:
1) Why do I have Hidden Web Parts? Where did they come from?
There are many reasons for this, one of them is that you deleted a ShortPoint design element that contains a Web Part.
Another possible reason is that you deleted the Web Part using the Edit Source button from SharePoint:
2) What is the correct way of deleting a Web Part from the Page?
Whenever you want to delete a Web Part correctly from a page, follow these steps:
1. Activate the Web Part by clicking on its title. Once you do this, you will see a WEB PART ribbon tab at the SharePoint ribbon bar:
2. Click the WEB PART Ribbon Tab, and then press the Delete button: