At first, I was confused seeing two marriages to women "de Montagu." Medlands shows Elizabeth having married Walter de Ufford, the brother of William de Ufford, 2nd & last Earl of Suffolk . I don't find evidence for William having married thrice with Elizabeth de Montague being one.
6. WALTER (-1360). m (1351) as her first husband, ELIZABETH de Montagu, daughter of EDWARD Montagu Lord Montagu & his first wife Alice of Norfolk (1344-1361).
https://fmg.ac/Projects/MedLands/ENGLISH%20NOBILITY%20MEDIEVAL2.htm...
Presently, a profile for Walter de Ufford has not been created and connected as a son of Robert III d'Ufford, 1st Earl of Suffolk , Owing to the marriage year (1351) that Cawley believe is in the ballpark, Walter probably was born c.1320. Robert would have likely preceded him in birth (named after his father) and Catherine was born first given FMG's suggested marriage year.
Here at https://our-royal-titled-noble-and-commoner-ancestors.com/p1470.htm... , the website shows William having married Joan 'Montacute' of unknown ancestry. So the website is in its present state errant and not useful for Joan.