It could be many things, plumbing to the engines, tank leak, ect. You could see fire on the control flap actuators, so the ship interior was engulfed in fire at the same time the first engine was out.
Yeah, most likely engine bay fire taking out systems one by one. Would be interesting to compare the telemetry cutoff with the video of explosion if possible. That could indicate if the fire even triggered an explosion, flight termination being activated or just reentry heating making the tanks explode.
I noticed that the CH4 tank level was much lower than the O2 tank level. That suggests a leak.
Given the huge spread of the debris, it must have been a decent sized boom, no? I mean that's got to be 10's of miles wide in this video.
https://x.com/adavenport354/status/1880026262254809115