There are a lot of different things that potentially can be going on. We had a couple things burn in the engine bay in the last couple test. What you are refer

There are a lot of different things that potentially can be going on. We had a couple things burn in the engine bay in the last couple test. What you are referring to however is most likely related to access gas. Starship starts up 3 engines, and then shuts down two of them to land with 1 engine. Both during the startup and but most shutdown, some amount of access methane escape from the engine. Since the other engine is still burning and hot, this access gas can start to burn. This is not all that concerning most of the time as long as there is not a continual leak.