In a 2016 trade between the Dallas Stars and Calgary Flames
Flames traded away Kris Russel for a player playing in Finland, another one playing in KHL and a conditional 2nd
The conditions
Conditions: If Dallas makes conference finals, and Russel plays 50% of games in first two playoff rounds, the 2nd round becomes a 1st round
Conditions were not met and with Dallas's 2nd round pick Flames selected Dillon Dube. Dallas used there 1st to select Riley Tufte who has yet to play a NHL game while Dube has 43 points in 121 games.
What is your example of this?

Montreal has apparently done almost 0 trades that involve conditional picks so I’d have to say the Drouin + Conditional 6th for Sergachev + Conditional 2nd since Sergachev is already better than Drouin and we later traded down with that 2nd and got Jordan Harris ( the conditions on both of the picks were that if Sergachev played less than 40 games they would transfer, he played over 40 games so we kept our 2nd )