While I don't have experience w/ TI and trigger I can tell you that I seem to have an issue with "empty" follicle for IVF, where I am growing a follicle, but when they go in to retrieve it for IVF, it doesn't come out. This has now happened to me twice, and it's super frustrating. And then on u/s it doesn't look like it collapsed. So, maybe this is what is happening? I think you said that you had a temp shift as well? ( I did as well.) So based on my experience, it seems like maybe the egg didn't come out, but it's producing progesterone and therefore gives you signs like you ovulated. I think LUFS might show a similar pattern, but not sure. It could also be that the trigger might not have worked. Did they say if they think the egg will still come out? Based on what I have seen others post in the past, it also seems like your p4 can rise and look like ovulation w/ bbt shift, but it hasn't really happened yet. I might be confused, but I think I have seen this happen to others here so maybe this will also happen to you. I also know that some women (Dr. C just told me this), and it's very rare, don't ovulate or have mature eggs unless they are triggered when the follicles are much larger than normal. In fact, they suspect I may be one of those women and next time I am going to trigger when my follicles are much larger.
I hope this makes sense...it's all very confusing and I think there a few possibilities here, so hopefully some of what I said made sense. If not, let me know