I also have a Tefal - not too bad - but slot size is a bit limited. However, I have found that sometimes after giving it a good shake to get rid of crumbs the lifter thing won't stay down to engage the element. Crumbs get on the pole piece of the magnet. I have become deft at taking it apart to remove the offending crumb.
I hope this helps if anyone else has the same problem.
Remember the days when a manufacturer would be interested and would take steps to improve things..................?