I think I found the solution. As I mentioned before there is a page with a number of timelines. Each item on the timeline is stored in a MySQL database with a ID number.
There’s a ‘live’ page and a copy in which I work. After copying there are two entries for each item in the database with identical ID’s. Some days ago the copy page would not save what ever I tried.
When I looked in the database I found that the identical ID’s had different content: there were a lot of double backslashes and the special characters where different, like this:
I wanted to know which page had the different content so I removed the ‘live’ page. After that the content of the identical ID’s was exactly the same.
I now could work in the copy page and save it with no problems. When I restored the ‘live’ page the content in the database was still identical and so far I have not had a single crash.
Probably this difference occured when I started working and accumulated causing more and more crashes.