2.1.34 had a fix for [regression] default starting ease factor for new profiles is 130%, but it turns out that the applied fix (for every deck with a default starting ease of 130%, reset it to 250% and reset any cards with ease below 200% to 250%) gets applied each time you do a force-sync with AnkiWeb.
It turns out that some folks recommend deck setups where you have 130% initial ease but an interval modifier of 192% in order to effectively disable the effect of ease factors (the idea being that it avoids ease hell). However if you ever have to do a force-sync, later versions of Anki will reset your options and cards.
I guess this happens because a force-sync does some sort of schema dowgrade then upgrade internally?