There is a 20% chance of a respin chance being triggered after every spin. If the respin chance is triggered then Astro Legends will do some tests to see if a respin will be triggered. First it needs to check if there is a winning combination of clusters that has been created. Second it needs to check that there is only one type of winning clusters created. If these two conditions are in place then the respin will take place.
When the respin is triggered the winning cluster will be held in place. If any symbols are added to this cluster or another winning cluster is created then the symbols will be held in place again. This continues until the reels are full of new symbols or no new symbols are added to the winning clusters. Once this occurs the win will be paid out.