Page disappears from tree/red triangle warning icon

Hi,

I'm quite puzzled by this. My client has a page that existed fine before. They have made a change and the page has disappeared from the tree. I have found the page again, but it doesn't show up in the tree, even after editing it and moving it to it's correct parent. I then searched for it again, and this time didn't edit it but moved it and it now shows in the right place. However, it has a red icon with a yellow triangle in it. I searched around but couldn't really find what this is meant to be. The page now shows up but when it gets saved, it disappears again. I have cleared the cache, no change to this behavior. So
- anyone knows what the red page symbol with the yellow triangle means?
- why does the page just disappear?
- how can I find out a bit more about what the problem is?

Help much appreciated as ever

Thanks

Doesn't ring any bells to me, but maybe you can take a screenshot of the icon / how it shows in the tree?

sure, attached now - makes any sense?