I am not a big jumper, just a little chop hopping. When landing, if the board is not in direct line with the direction of travel, you will always spin out. When the fin lands a bit sideways = spinout. This is pretty common, so you have to learn to turn the board in the air a bit downwind to get a landing without spinout.
In upwind sailing, too much back foot pressure on a fin, especially at slower speeds will push the fin sideways and cause spinout. A bigger fin or more speed will help, but it's learning the limits of pressure on the back foot that is the most important. The faster you go, the more pressure you and put on the fin.
Some fins spin out more than others, but it's your sailing technique that is the most important.
I am not familiar with the stock fin on a Kombat 105, but if you will share what fin you are using and its size, others may be able to help you as well.