[TYPO3-mvc] Repository does not always insert values

[Wim]

Typo3 version: 6.2.12
In a http request a row is inserted via the repository. The column values in the row are filled. No problems.
In a Ajax request (Eid) the content of the repository is read. The column values are received. No problems.

But.. After a rest of an hour or so, I activate the ajax request, the row is read but the column values are empty.
Doing the http request, a new row is inserted, but the column values are empty (although NULL is not allowed for two columns).

Clearing the caches does not solve the problem.

The only solution that works, but not practical for sure, is uninstall an extension and install that extension. 
After that, the repository works fine again. Until for a certain time there are no requests for the server (I use a local XAMPP server).

Has anyone an idea how to solve this annoying situation?