Since updating from 4.12 straight up to 4.17, our long-running 4.x installation has become funky. Randomly, to our minds at the moment at least, changes to questions do not get saved. This happens consistently to all dropdown questions with a red bar appearing at the top at the attempt to save the question, which contains no text at all. It also happens inconsistently to most other question types when adding or changing translations, though the question gets saved and the saving is confirmed, with the caveat that the changes do not get saved.

Console errors include:

• Failed to load resource: the server responded with a status of 500 (Internal Server Error)
• ResizeObserver loop completed with undelivered notifications.
• PJAX -> – "No JSON found. If you expected it there was an error"
• TypeError: null is not an object (evaluating 't.instance.destroy')
• TypeError: null is not an object (evaluating 'e.id')

When trying to turn on debugging in config.php, Dropdown questions do not load at all, without any error in browser consoles or error log files.

We had surveys running on 4.x with dropdown questions, and had no problems with that particular question type nor with any other questions.