As you may have heard, the text widget in 4.8 is SERIOUSLY broken for any text widget content with raw HTML or scripts you may have previously created.
They apparently have “fix” (not a good one, in my opinion) in 4.8.1 (no release date yet scheduled) that will detect if html was added in the old text widget and then switch to text mode, and give you a nice big warning that you should really move all that code to a new HTML widget to be added.
For some reason, the WP developers just don’t seem to understand that there are at least tens of thousands of existing web sites with maintainers who don’t want to convert millions of text widgets to html widgets. They have a real problem with what has been standard WP practice over many many years to include custom HTML and script in the old perfectly good text widget. And they simply refuse to give even a tiny admission that they really screwed up.
Very disappointing response from WP developers.
What to do?
So, if you have text widget with custom HTML/script code, you WILL have to convert them to a different widget eventually. So for now, the choices:
If you have already upgraded to 4.8, do not open text widgets with raw HTML or script until 4.8.1. This seems to be the only easy path for anyone who upgraded to 4.8. This is what I am doing.
If you’ve upgraded to 4.8, or want to, get the replacement legacy text widget, and follow the conversion hits that can be found on the web. This will leave you “stuck” using the legacy text widget forever unless you want to convert yet again to the coming HTML widget.
Otherwise, wait for 4.8.1, and hope WPs hack to detect presence of HTML/script will actually work and prevent them from breaking. Then manually convert on an as encountered basis to the new HTML widget.
Even though the WP developers seem to be refusing to admit any mistake, there is wide spread agreement that this is one of the worst “improvements” that WP has ever made!