The early post made mention to possibility of a 120V EV charger being used in the garage. Is one of those burnt wires belonging to the garage circuit?
The picture looks to be a subpanel, has the N/G bonding been lifted?
Are all the EGC are on the one side that have the burnt wires? YES
Have you confirmed that each neutral only serves just the one circuit? Have seen where a junction box was made up with multiple circuits run through that someone tied all the neutrals together. Seen as many as 4 circuits brough together is such a way. If one of the circuits was to loose its neutral path to the panel the other neutral would simply pick up it's load and the Home owner would never notice and issue because of the splice everything would continue to work. But if the combined loads being shared under the remaining neutral was to exceed the rating of the wire it would heat up maybe even burn. it would never trip the breaker as the breaker is only seeing the loads of the "hot side" not of the neutrals.
I would expect to see heating evidence on most of the length not just at the termination, but wouldn't rule it out if other things have been checked.
Most likely is loose connections. You state that all the connections are tight. Not to be insulting but how was this confirmed? Did you just try to see if they would tighten anymore? Use a torque wrench or driver to verify mfg specs? Did you actually back them off? With this much burn I wouldn't be surprised if the screws are seized and seem to be tight, and wire actually welded in so seem to be tight. (seen it) These wires need to be removed and stripped back to clean insulation and re-terminated anyway. That bus is compromised at best now, and I would think the inspector could ask that it be replaced with that much damage.
Been seeing issues with the mfg. of the bus screw or bar so that they seem tight before you even start, hitting the torque spec without even getting the wire slightly held. One was hitting the 20inlb (Eaton BR specs) without even turning the screw at all or wire even under the screw. Also, been having to run them in and out multiple times before you can get them to torque. Been a bigger issue more recently.
