Higher than normal heart rate for FTP zone

Hi.

What does it indicate to if my heart rate is like 10 beats higher for the same power zone for an activity i did a week ago. Does this mean i am fatigued?. I do feel more tired than normal but just need confirmation if this is normal?.
I am not sick or anything like that, i have the same diet and follower same sleeping patterns

Usually high fatigue means higher resting HR and lower interval HR

Yeah, that is what i read too, i tried to google it but cannot find any info on when the heart rate is unusually high based on power. Maybe one of my meters was playing up, i was hoping somebody experienced this phenomenon too.

On the weekend i did 3x20 outdoors in the cold at or around FTP and the difference in BPM compared to indoors was about 10 beats lower. Heaps of factors including fatigue.

Is the temp the same week to week?