PCBgogo

I just 3D printed a pair (or though I did) of 45 degree brackets for my Asus portable monitor. I plan to use the bracket to hold the monitor tilting downwards for me to see more clearly (the monitor sits on my giant 12" scope).
I managed to fit 2 models within the printing area, and I did a test print. The first pass it printed, but something went wrong. I modified support structure and gave it a second go, and this time it worked.
What was bizarre is the second print only yielded one part. The monitor LCD showed 2 parts being printed, and I double checked the sliced file and indeed it has two models in it.
The second part simply vanished -- not to be found on the platform, not floating in the resin tank, and not stuck on the bed. The second part simply vanished without a trace.
Naturally, I suspected if half of the LCD was broken and only half of the printing area was exposed, so I did a UV test. It turns out the lithography LCD and the UV lamp are all fine.
So, what could have happened?
The printer is an Anycubic Photon, with stock green resin. I would like to give it another try with some engineering resin, I would like to know what happened to my previous printing?