Somewhere between WP 5.5 and WP 5.7 upgrades, on my wp-admin page strange pure text “close” link started to appear at left upper quarter of the screen. The position of this link slightly lurks between refreshes/redraws of the screen (clicking a link or an element). It looks like this “close” link appears over some of the links or other page elements, so it is possible to click some links/elements but the rest are like inactive. When I click this “close” link, it disappears and all links/elements become active, until next refresh/redraw of the screen.
So, if someone have had any problem like mine, give me a hint, please!
Thank you in advance!