I have an issue, that a few shapes (in this case Russia and Australia) has a line that spreads accross the globe. I cannot select the line individually and when i select Russia, the line by Russia is automatically also selected. In the attribute table, it just shows up as one shape. How do I solve this?
The problem is that your central meridian is 0 degrees (greenwhich). russia e.g. goes "beyond" 180 degress east of greenwich. you can find a solution for this problem here: How to dissolve naturalearth vectordata with gdal?
Maybe it's a mulutipart feature? In ESRI, you would explode the feature, but I believe in QGIS there is the "Multipart to singleparts" tool.
Once you've separated the two features, there should be multiple entries in the attribute table.
If another feature doesn't show up, then it might just be a geometry visual glitch. In which case, if you don't need exact boundaries, you may be able to get it to go away by simplifying the feature geometry.
I merged two different maps with different CRS. It solved the problem to make sure they merged on the same CRS.