At time of booking Swiss.com makes an authorization on the credit card and after 24h the settlement is sent. When the system can't match the authorization with the settlement due to small differences in transaction amount (in CHF) a new authorizations is made and the transaction is immediately posted. You either need to wait 10 days until the first authorization is cleared from the system or asking swiss to void the authorization based on the authorization code. Second option sometimes do not work either. Usually credit card company policies do not allow to delete authorization by them self as in this case, there are taking the risk.
It is a bit tricky if you have just an available balance for one transaction and not both, this leads to the issue that the transaction after 24h is rejected. This behavior is generally a topic of your cc issues an not swiss.com specific, I had it a couple of times with SQ as well.