The forks happen when there are slot battles or height battles. You can see the forks in the logs of your node.
This is an example of a fork caused by a height battle (2nd block was produced by a block producer before it received the block minted one second before, and in this case, the second block was selected by the nodes to be the correct chain):
[2022-01-24 06:24:14.24 UTC] Chain extended, new tip: c7608663d90328f91df9dee824f55e9ee30411a8bb3794befb06357b520b3513 at slot 51439161
[2022-01-24 06:24:14.24 UTC] Block fits onto some fork: 18cd19d5af692f296494d041b4b6742cefaad7f6690da553dd0e60087237388c at slot 51439162
[2022-01-24 06:24:14.49 UTC] Switched to a fork, new tip: 18cd19d5af692f296494d041b4b6742cefaad7f6690da553dd0e60087237388c at slot 51439162