I have retest it and found that Mangudai attack stat will disappear after research Improved Siha bow or Incendiary arrow (both upgrade finish in close together so I’m not sure which one).
Improved Tithe Barn research didn’t get any resource other than larger gold.
This one I still unable to replicate it but maybe involve with capture sacred site after research tithe barn.
By the way, Improved Siha bow upgrade didn’t disappear after upgrade still there.
Thanks @Narute00100! Let me know if you experience #2 again, but we’ll look into it. The other two bugs mentioned here the team is already investigating. Much appreciated!
Sadly it still happens!
I was trying to get the actual event done.
I can’t tell, if Tithe Barns was actually researched, but I did research Monastic Shrines.
Later I saw that the Normal Tithe Barns was missing (as if it were researched) and the Upgraded Tithe Barns was grayed out, with "Requiremets: ". No wood or other income at all, only gold, which really can hurt the mongols, when they need more stone.