Recent update not compatible WP page editor

thanks for your reply. The only error logs I can find on my host’s server are below for today’s date. The latest (topmost) is the error that came up after I tried to “add new” page while the plug-in was activated, giving me a blank/white screen and no editing tools in the right-hand column, as one usually sees. Strangely, this is only happening to the page editor and not to the post editor, which is working fine. Most recent error log listings:

2020-12-21 03:19:21 UTC [nginx][error] 51432#0: *587947 openat() “/home/u321-3vh3kmfrqaww/www/mfjustice.com/public_html/.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt” failed (2: No such file or directory), client: 172.69.25.69, server: mfjustice.com, request: “GET /.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt HTTP/1.1”, host: “mfjustice.com”
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2020-12-20 23:19:07 UTC [nginx][error] 59167#0: *406738 openat() “/home/u321-3vh3kmfrqaww/www/mfjustice.com/public_html/.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt” failed (2: No such file or directory), client: 172.69.26.7, server: mfjustice.com, request: “GET /.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt HTTP/1.1”, host: “mfjustice.com”
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2020-12-20 19:19:02 UTC [nginx][error] 96697#0: *215780 openat() “/home/u321-3vh3kmfrqaww/www/mfjustice.com/public_html/.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt” failed (2: No such file or directory), client: 172.69.26.147, server: mfjustice.com, request: “GET /.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt HTTP/1.1”, host: “mfjustice.com”
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2020-12-20 19:07:42 UTC [apache][:notice] [pid 86504] [client 47.143.84.91:44606] mod_hive matched URI http://www.mfjustice.com/wp-login.php (/home/u321-3vh3kmfrqaww/www/mfjustice.com/public_html/wp-login.php) with match 2, referer: https://www.mfjustice.com/wp-login.php?loggedout=true&wp_lang=en_US
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2020-12-20 15:18:51 UTC [nginx][error] 86733#0: *12855 openat() “/home/u321-3vh3kmfrqaww/www/mfjustice.com/public_html/.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt” failed (2: No such file or directory), client: 172.69.26.18, server: mfjustice.com, request: “GET /.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt HTTP/1.1”, host: “mfjustice.com”
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2020-12-20 11:18:37 UTC [nginx][error] 27181#0: *3773831 openat() “/home/u321-3vh3kmfrqaww/www/mfjustice.com/public_html/.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt” failed (2: No such file or directory), client: 172.69.29.36, server: mfjustice.com, request: “GET /.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt HTTP/1.1”, host: “mfjustice.com”
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2020-12-20 07:18:34 UTC [nginx][error] 73347#0: *3607137 openat() “/home/u321-3vh3kmfrqaww/www/mfjustice.com/public_html/.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt” failed (2: No such file or directory), client: 172.69.26.7, server: mfjustice.com, request: “GET /.well-known/pki-validation/ca3-1c0a84368e93472f9db9cfd3f40c85ff.txt HTTP/1.1”, host: “mfjustice.com”
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2020-12-20 05:53:37 UTC [apache][autoindex:error] [pid 65430] [client 2600:3c02::f03c:91ff:fe69:4b66:58512] AH01276: Cannot serve directory /home/u321-3vh3kmfrqaww/www/mfjustice.com/public_html/wp-includes/css/: No matching DirectoryIndex (index.html,Index.html,index.shtml,index.php,Index.php,index.phtml,Index.phtml,index.htm,Index.htm,home.htm,Home.htm,default.htm,Default.htm,default.html,Default.html) found, and server-generated directory index forbidden by Options directive

To the best of my recollection, the sequence of events that caused the problem went as follows:

Dec. 19, 2020:

1. Logged into my WP account.
2. Updated CAS plugin.
3. Began working on website, including my “Subscribe” page. It opened fine in the page editor and went back and forth a couple of times between WP’s page editor and the UX-Builder editor (the Flatsome theme editor). At one point, while I had the page open in the WP editor window, I clicked on the “Settings” button (the little gear-shaped icon) in the upper right-hand corner of the window. The “Settings” button toggles on/off (opens/closes) the right-hand column toolbar. When I clicked on the settings button, instead of closing the toolbar, it made the whole window go blank, and all the function buttons above the toolbar disappeared (only the “Preview” button is visible but it is not functional–nothing happens when you click on it.) The gear-shaped “Settings” button, the “Publish” button, and the three vertical dots for “Options” have all disappeared. As you can see from the screenshots, in the “with CAS activated” there are still the tool buttons on the top of the page on the left side but none of them work properly. If I click on the plus icon to add a block, then choose one (for example, text), nothing happens, the editor window still remains blank. I can still click on the UX-builder button and it works (opens up the UX-builder).
4. I have the “All in One SEO Pack” plugin that appears below the blank window area but all the text boxes have disappeared, so that plugin is rendered nonfunctional as well, due to the CAS plugin. Below the “All in One SEO Pack” is the “Custom CSS” box which appears to be working, the “Page Layout” which is nonfunctional (no dropdown selection menu), Page Footer (selection dropdown menu IS working), and lastly, the “Sidebars – Quick Select” dropdown menus (working). Normally, the Page Layout, Page Footer, and Sidebars-Quick Select should appear in the right-hand side column when the “Settings” gear icon button is toggled ‘on’.

Again, NONE of this is happening in the Posts editor–everything is fine. It is only the Page editor that has been broken by the CAS update.