With only 250m to go, Jennings looked every inch the winner ahead of German Nina Gaesler but then disaster struck.
Jennings hit something and stopped dead in the water just metres short of the line, falling from first to fourth at the finish.
Gaesler took the title with Jo Hammond staying on for silver and Finnish Sculler Mina Niemeinen picking up her first world medal with a bronze.
Timmy Harnedy lined up in an extremely competitive B final and put in a classy performance to take second, a mere eight hundredths of a second behind the winner, Russian Denis Moiseyev.
The Irish Lightweight Quad, made up of Limerick men Brian Young and Kenny McDonald, Galway native Herbie Griffin and Kildare’s Diarmúid McColgan, put in a good row in the B final to take second 2nd place behind the more experienced British crew.
There was further disappointment for Irish Lightweight Pair Neil Casey and Derek Holland, forced to withdraw from their B final as Dubliner Holland suffered a recurrence of the infection that cut short their participation in Lucerne at the World Cup last month.