I have always interpreted the Investiture of Flame spell as having a flamethrower effect, similar to Aganazzar's Scorcher, but one of my players pointed out a different interpretation.
Here is the relevant segment of the spell:
You can use your action to create a line of fire 15 feet long and 5 feet wide extending from you in a direction you choose. Each creature in the line must make a Dexterity saving throw. A creature takes 4d8 fire damage on a failed save, or half as much damage on a successful one.
My player pointed out that the spell as a whole is Concentration, up to 10 minutes, while no duration has been specified for the line of fire. That has led them to believe the lines of fire stick around.
I believe this is just poor wording by the writers, who were assuming the reader would interpret it as an instantaneous effect, rather than a hazard-creating spell because such spells almost always have the clause "deal n damage when a creature begins its turn there or enters it for the first time on its turn." Nevertheless, I wanted to double-check to make sure I wasn't severely underpowering this 6th-level spell.
How long does the line of fire last? Is it instantaneous, or does it remain there until the spell ends?