Hi Frkn64,
You are welcome.
Could you change the Theme and apply the other and see whether you get the same Notice on your Page, also check it by changing the Designs? Are you sing any Cache? (Try clearing Cache and check)
Let me know how you’re trying to add the Widget as the same is not being displayed in Non-AMP Version.
You can find widget Option in Appearance –> Widget.
I deleted my WordPress and made everything from scratch again. And the problem is gone but thanks anyway for your reply. 🙂
Hi Frkn64,
You’re welcome and I appreciate your effort.