You haven't posted a link for your current source of the data. I am left guessing and trying to recall what you've used in the past. It's a bit of a trend for you not to link your sources as often as not.
You are having a lot of difficulty accepting that glaciers loose ice by creep and ablation. Surface ice accumulates so that plane will be covered deeper and deeper. Glacier loss is by ice creep to it's terminus, so ice is lost from underneath. So that plane crash is initially on the surface but will be deeper in surface snow over time. And you'd expect it to eventually also move down the glacier.
Your surface mass charts are effectively only showing how much it's snowed. And snow may increase with a more moist atmosphere and freezing conditions still most common at the altitude of the top of glaciers. Changes in weather patterns may affect that also though.
But if the lower areas of the glacier, at lower altitude are warming, then ablation and glacier ice loss will increase. Which is what the science shows is happening. Overall glaciers are loosing ice mass.
