After having pulled out more than half of my hair, I finaly found the cause – earlier Enfold versions allowed (by using Avia layout builder) to use smaller layout elements inside bigger layour elements, in other words to nest them. For example 1/2 layout element could fit inside three 1/3 elements. The page in question was created when such nesting was possible, but now the page wouldn’t update and save the content changes. As I understand the Grid Row has now taken over that functionality.
However, a new problem arose: the Grid row takes up 100% of visible width of the page (100vw), although this contradicts my settings in: Theme options > General layout > Layout > Stretched, and at the same time > Dimensions > Responsive Site “checked” > Maximun container width > 1130px. In other words, in all of the website pages, the #main container is set to have a max width of 1130px, but the Grid row won’t obey that. Now, other layout elements, which are not the Grid row, nor inside it, behave normaly – for eksample a 1/1 layout element/block is precisely 1130px wide. I know i could fix it with css, but that would be a tiresome labour in the long run. Any suggestions?