After my workout today I received a Nice Ride! email (which is a great feature btw) with an updated threshold HR:
Your threshold HR has increased by 2 to 163 bpm from 98% of 20m at 168 bpm
98% of 168 is 165, not 163. The note on the activity on the intervals.icu website looks like it has it correct:
Threshold HR +2 to 165 bpm from 98% of 20m at 168 bpm
Maybe the email is using the previous threshold HR and not the updated value.