Electrical wire nut melted
Why do you tape the wire nuts?
I can't speak for you... but generally... The usual reason people tape wire nuts is because, in their experience, the splice falls apart if they don't.  Well, if they fall apart that easily, it is a defective connection that is prone to arc faults.  Arc faults make a LOT of heat and will do just that.
The other thing about taping wire nuts is, they preclude doing a pull test.  You can't do a proper pull test on a taped nut.
A pull test is, hold the nut very firmly, then pull on the wire so hard that the nut slips out of your fingers.   I'm talking really hard.  Do that for each wire.
Tightening &quot;really hard&quot; is good, but not conclusive.
The problem is that certain craft errors assembling the wires can cause the connection to fail even though you tightened really hard.  E.G. the wires are not even (staggered) when inserting them.  Stripping too little will also do it.
Here's how you can &quot;post-mortem&quot; whether that was the problem.  Go back to all your other wire nut splices that you've ever done, and give them the full &quot;pull test&quot;.  From that, you will have a sampling of how good your wire-nut splices are.  If you have any fail, that suggests technique may be the root of your problem.
Abandoning wire-nuts for other splice techniques is like learning how to ride a bike, and quitting the first time you fall off.  You can't learn until you test and pay attention to the feedback the test gives you.