I write all my Zwift rides in a Excel Sheet shortly after riding.
my.zwift.com says, 4623km and 54034 climb meters.
My Excel Sheet says 4730.5km and 55379 climb meters.
The rides that were not saved correctly cause of a PC Problem are not included in the Excel Sheet.
I’m missing 107.5km and 1345 climb meters.
I noticed this long time ago, but it don’t really bothers me.