I just had the issue (today at 9.49 am, Brussels time) , when I consulted my activity of 15/11/2020.
I checked carefully what I did :
- I consulted the activity of 15/11/2020, and especially the elevation data and the related graph (which is a really nice feature btw), I checked the data (% of elevation) of different climbs
- then I consulted another activity
- then I went back on the activity of 15/11/2020, and everything was gone again.
I did it on my tablet, browser Opera.