Can confirm that ransoming your explorer in multiplayer causes a desync in Windows 10 and AoE III DE 100.13.27885.0.
Happened twice in a game with a friend before I realized ransoming my explorer was causing the desync. (Side note, we had the AI on extreme difficulty for this match and it felt like we were on normal - they hardly fought back at all.)
Got this issue too. Played 2 multiplayer matches now where it both happened. First time it happened because someone else did it, then second time I thought it wouldn’t happen, so I ransomed my explorer and boom, directly the game goes out of sync. PLEASE FIX THIS, the game is unplayable now!
I am also experiencing this issue too and so is my friend, we thought it was DLC download as seems to happen on other unit delivery cards too for us. but 100% of the time we desync if we ransom hero back to life. Please fix this soon