Seems like this is a Visualforce page as per the screenshot provided.I would suggest you to check,if you have override the standard page with any other page on the Object buttons page.
Otherwise,you can look for the page name lookupPage in the visualforce page which can I see in the url.
Please mark it as best answer if it helps you to fix the issue.
Greetings!
Seems like this is a Visualforce page as per the screenshot provided.I would suggest you to check,if you have override the standard page with any other page on the Object buttons page.
Otherwise,you can look for the page name lookupPage in the visualforce page which can I see in the url.
Please mark it as best answer if it helps you to fix the issue.
Thank you!
Regards,
Shirisha Pathuri