This type of issue indicates that the contract of a block includes transition which cannot happen due to the defined behaviour of this block.
You can either remove the unused transition or change the block’s behaviour so that the transition can take place.
An example of this type of situation is depicted in the following figure.
The analysis will report the error Transition stop/stopped never used, as this transition is not possible due to the defined behaviour of this block. To solve this issue, either remove this transition or make it possible by changing the behaviour (e.g. removing the timer).