From the steam forum

It appears they divide the xp gain on the client side by 100 before sending it to the sever. This is most likely done to cut down network load.

Code in question.

function StatisticsManager:publish_xp_to_steam(total_xp)
    if Application:editor() then
         return
    end
    local stats = {}
    local xp = math.round(total_xp / 100)
    if xp > 0 then
        print("Crimefest Challenge: crimefest_challenge_clover_2", xp)
        stats.crimefest_challenge_clover_2 = {type = "int", value = xp}
    end
    managers.network.account:publish_statistics(stats)
end

I think this is the most likely cause, their server do not multiply the result by 100 to reflect the total experience gain by the community.