Loud "thunk" sound each time my shoes pass the 1 o'clock position with both shoes
My bet is that this is caused by the bike rocking side-side as you shift body mass and pedalling forces. The noise is caused by the trainer shifting or perhaps the bike frame shifting on the trainer. The vibration or noise is coming through the frame and feels like it is emanating from the bottom bracket area.  

Its sounds like you have ruled out the noise coming from the bottom bracket / crank area. I would spin the crank by hand with the bike in the trainer to make sure of this. Also grab the crank arms and push/pull in all directions to check for any play or movement in the bottom bracket.

If you have a smart trainer check that its axle does not have any play.

Try sitting on the bike and shifting it side-side, as if you were sprinting, but without rotating the pedals. Can you replicate the noise this way?

Can you ride the bike off the trainer to see if the noise occurs then also, or goes away?

Can you recruit a friend to listen and try to locate the source of the sound while you ride the bike? (Being careful to not get kicked in the head or tangled in the drivetrain of course.)