I’ve been experiencing this issue with this specific website quite often. I moved it from a staging domain to the production domain and since it’s been doing this. It did not do this on the staging domain (same server).
- I did a find and replace on the database to ensure that the staging domain was replaced with the production domain.
- I have flushed the permalinks.
- I have increased PHP memory for this site
I can’t point to a specific plugin. I’ve used these plugin before on many sites. Everything is up to date. I have not found a pattern to when it appears. If I click between the Posts, Media and Page tabs often enough it eventually happens. I also happens when interacting with the plugins section of the site.
After it has happened a refresh of the page brings it back.
Here are examples: