Thank you for looking into it - the hills do seem to have stopped vanishing when making an edit, which was the most disconcerting thing,
They shouldn't vanish when you edit. However, if you select to tag your report to a walk route, all the hills are reset to the ones included in that walk route. So if you tag the route first, the hills will be filled for you; but if you tag some hills and then choose a walk route (that doesn't include those hills), then the ones you tagged will be overwritten, if that makes sense.
I'll look into the loss when previewing, may be able to do something about that.