Can’t let me install/update themes and plugins

I am facing various issues in wordpress. Whatever the issue I faced, I wrote it down below in sequence.
First of all I went to the page that I wanted to edit. It was built with elementor. So I clicked “Edit with Elementor”. The page loaded but elementor widget section didn’t. I thought there was problem with elementor.
Then I went to “Installed plugins”, there I was unable to update or install the plugin. It says “Update Failed -1”. Same thing happened with theme. I was unable to update or install the theme. Then I went to Appearance > Customizer. There this message was shown “non-existent changeset UUID”. I have a managed wordpress. It was working till last week. After that with no reason the above issues popped. I have searched for many solutions but none of them were related.

It would be of great help if this issue is resolved.
Thank You.

The page I need help with: [log in to see the link]

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