Workout didn’t record the actual time

I completed outdoor walk for nearly 80mins and the exercise summary shows the actual time, but the exercise ring is only recorded for 15 minutes. Why is this happening? It hasn’t happened for a while, but earlier I remember it to be occurring like one or two times, what could be the reason for this year? Is there any fix to update the time to the original workout time? BTW I use an Apple Watch Ultra 2