In 1396 he campaigned against the rebellious West-Frisians together with Albert I, Duke of Bavaria, and in 1398 he made a pilgrimage to Ireland to visit the St. Patricks Fire.
Jan entered the monastery Zeelheim in Diest as brother-abbot with the intention of putting his remaining life in the service of God.
William's brother Gijsbrecht having died two years before that, the title and domains of Abcoude fell to Jacob van Gaasbeek, a nephew of the family.
In the spring of 1409 Jan, with the intention of challenging Jacob van Gaasbeek's inheritance, resigned his position as lay brother so that he would be eligible for the title and domains of Abcoude, but he needed his wife for that as well.
Unfortunately the English commanders were aware of his past and refused his entry, after which he travelled to France and joined their army.