This might be because the same note was already input at the beginning of the first measure, but the gate time of the last step was set to “100”.
In this case, the last step is connected to the first step of the first measure with a tie. If you want the note to retrigger when the pattern returns to the first measure, set the gate time of the last step to a value of “99” or lower.
For details on how to edit the gate time, refer to “Editing a step”.