Hi @radimdrinka,
the first measure returns you the date when the first transition to KS happened (not particularly from SMB, it could be also from value ‘(none)’). If the change has happened several times, then it will still return the first transition for this field.
There are also other measures you can use, like, transitions from, transitions to issues count, transitions from issues count, and a few more transition timestamp related measures to find the first and last timestamp when your field was changed.
But if you want the transition from one value to another, then you can check the solution my colleague has provided on a similar question here and try that solution, as those changes won’t be easy to calculate: