Hello!

As Tutturuu said, probability/chance does not increase as each event is not connected or influenced by other events. This means that, regardless of how many times a ninja attacks Sasuke, their individual event chance of getting feared remains 50%.

An example would be a coin with heads or tails. If you flip the coin twice, regardless of what you get the first time, you will still have 50% chance to get either heads or tails on your second flip.

In the future, instead of making assumptions, I recommend asking the community first. The Naruto Online Community is a great resource and they try their best to help.

Also, if you do have any concerns in regards to bug or issues in the future, you can definitely report it in the Bug/Support section.