If you log off while you are mounted on a Strider that is currently in the lava (even though you are not) and log back on, you are lit on fire instantly while riding the strider. After 1-2 seconds, you start taking burning damage from the fire.
This happens in Survival, Creative, and Adventure, but the player is only on fire for a tick when logging in Creative, similarly to when a player dips in lava.
This bug also affects non-fire resistant entities riding on Striders.
Here are examples in videos: