I’ve had several lightning strikes. The bolt may weld small holes in the skin of the airplane. Some arcing of electricity may occur inside. Usually no real damage. It can make a loud noise heard inside the airplane when it hits.
The main reason I’ve been thinking lightning was the cause is because of the sudden loss of communication and no distress call. Something knocked their comm out and lightning is just one possibility to consider. Was the first one that came to mind.
Lightning probably strikes planes a lot more than most of us are aware of. The fact planes aren’t dropping out of the skies left and right says a lot about how well the built in protections work.