Suddenly unable to hold temperatures

A little under a year ago I upgraded my QU-BD TwoUp with a Lite6 and was extremely pleased with the quality of the extruder and the results it was giving. I didn't have any problems with it at all until about a month ago when all of a sudden it started having issues with maintaining temperatures.
As you can see in the images I've attached, the temperature was jumping all over the place really drastically and it was a pretty serious issue, with temperature readings as much as plus or minus 40 degrees from what it was set to be (with readings as high as 270 at times). I assumed this simply meant my thermistor was the issue, but all my connections seemed to be secure and I didn't know of any way to actually test if it was going bad for some reason.The other really weird aspect about this issue (and part of why I didn't think the thermistor was necessarily the cause) was that it was extremely inconsistent; sometimes it would hold temperature fine until it actually started printing and only then would it go crazy, other times it would hold temperature fine up until a certain temperature (as seen in image 3), and so on. For the most part however, the average temperature would be more or less where I needed it to be and the crazy readings would often work themselves out, so I foolishly kept printing and just wrote it off as a weird bug with the recordings or something.
This worked out fine with the exception of a few prints here and there that would cancel because the temperature was reading too high and causing an error, until earlier this week when I noticed the smell of the plastic burning as it preheated. Just putting my finger near the hotend was enough for me to tell that it was way overheating, so I immediately killed the power and let it cool. After a little bit I cautiously booted things back up and hoped that that was just a fluke, but after just a minute I could tell the same thing was happening. Before I could shut things down, there was a popping noise, a spark, and a lot of smoke from the hotend and I could tell it was really really hot. I haven't touched any of it since or tried to asses the damage because I'm a little scared to do so. I'm assuming the PTFE barrel is melted and I wouldn't be surprised if I shorted something on my board too.
I'm not entirely sure where to go from here. What do you guys think went wrong initially, and what do you think went wrong this last time? How much do you think is broken and will need replaced? Is this something I could try and still fix or will I need to just get new things? Is there any chance that this is all the result of something failing on the hotend and I will be able to get replacements from E3D, or is it entirely my fault and I'm going to have to buy new things myself? Thank you in advance for any help or suggestions you might have, I really appreciate it. Please just let me know if there's any more information I could provide to help or anything else. Thank you!

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