Project-GC update its data to improve the data, not to mess with people's statistics, obviously. Now I can understand the frustration, not the least when traveling fairly far for a specific geocache to fulfill something special. However, we prioritize correct data, as much as we can.
When it comes to elevation data it's quite unreliable overall. Over the years there are coming more and more technology to resolve the issues, better services becomes available and the data improves. Sometimes it's however that 80% of the data improves, and 20% gets worse. One can of course discuss what level of improvement should be required to change numbers though.
But in this case, as I understand it, it's an improvement of data, showing more current data, which should match the reality better. It's an active mine site, where masses are moved from one place into another over time. If I understand it correctly, there has been a big hole where GC3T13G is plotted, but nowadays there isn't. The old data showing -200 meters seems to be obsolete.
Here is a screenshot showing elevation data of the area as our latest service sees it. It seems to match this Lidar data as well.
If the cache owner wants to keep the -200 meters the cache icon needs to be moved further south east. That requires that the final isn't too far away, and of course that the mystery solution doesn't depend on the original location.