Truncate page on edit

When placing a page in editing, we have truncated content and, in some cases, it seems that it is mixed with the TinyMCE html code (See image below).

If you cancel editing, the page is displayed correctly.
There is no error entry in the plone logs or in the browser console (javascript).
When copying the html code through the browser, putting the page into editing, and saving we no longer have the problem in the next editions. I am without direction to look for what causes this problem. Has anyone been in a similar situation?
This site has hundreds of pages and few have had this problem. We have a server with a zeo installation of plone in version 5.0.8 and python 2.7 with hundreds sites. So far only 5 sites have had a similar problem. However, I am afraid that the problem will start to happen on all sites.