Technical Fuel tank issue

[Toby101]

Filled up today while the tank was quarter full and was able to 75l in. Never been able to put more than 60 in even when nearly empty. Drove with the gauge saying it can't read. After 200km and a restart the gauge went to full. After about 400km gage started coming down. I think I've worked out its something to do with the restriction to 60l as its on a motorhome.
Why would it suddenly do this and should I be worried about damage?

 

[jackwhoo]

The interior plastic tube extension that restricts fill volume has fallen off.
Nothing to worry about.