I don't think that oxidation is the main cause of the flavor turning extra bitter and burnt. This wasn't a highly hopped NEIPA, so it shouldn't be super sensitive to it. That would be more likely to have it go extra sweet and darken noticeably along with the hop flavor loss. Has the beer turned a lot darker?
However, I would expect the hop flavor to fade quite a bit, as it is 5 and a half months from bottling day. I wouldn't call almost half a year a short term change.
It could be an infection - are the bottles becoming more carbonated and foaming a lot when opened? Is it consistent with all bottles, or sporadic with just some? Do you disassemble your spigots for cleaning and sanitizing?
It could be a combination of several things. It could be that the hops faded, allowing a water problem to become noticeable, with a concomitant infection. What's your water like and how do you treat it?
Do you want to start chasing cold side O2 reduction? If you have been happy with your other 15 batches up until now, and it's just this one batch that has problems, oxidation probably isn't the problem you are noticing unless you did something different this batch. I have gone fairly aggressive in my cold side O2 mitigation, and it made a difference for me, but like everything in homebrewing, everyone has their own preferences that they should brew towards.
People here are pretty passionate about homebrew, so you are likely to get some good troubleshooting help from several perspectives.