WP site does not stay in EDIT mode anymore after install of Yoast SEO plugin

I am new here and have no experience with forums so I am sory if I am not at the correct place. After I tried Yoast SEO plugin, my site does not stay in edit mode anymore. I removed the plugin but my site still does not stay in edit mode. I did a re-install of the latest WP update, I deactivated all plugins and activated them again. Problem is still there. My Theme: Twenty Seventeen Child, Current version: 5.6.2 Sorry, but I do not know anything about code or files the site is made of. My website is hosted by Underhost-Canada and has C-panel I use for back-up. Thank you for your help.

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