This is the most common one I get. The airflow ring sits right where you twist to adjust draw resistance, and that twist action can work against the seal. Here's the checklist I run through with most people:

Power off and disassemble. Take off the mouthpiece and pull the airflow ring off if your device lets you. Wipe down all the surfaces with a dry cloth. Often the leak is just pooled condensation, not an actual seal failure.

Inspect the O-rings. These are the rubber circles that create the seal. Look for cracks, nicks, or if they've rolled out of their groove. A misaligned O-ring is the top cause of leaks at the connection.

Re-seat gently. Don't yank. Use your fingernail to nudge the O-ring back into place. Then reassemble—finger-tight is enough. Over-tightening squashes the ring and breaks the seal.

If the leak stops, you're done. If it doesn't, move to the next step.