Bug with slicing slices

I use a python script to script to extract pressure signatures at different radial distances at a couple of angles - it usually works but today I got a garbled solution.
I normally get results like this:
waveform_phi_0(1)

but I got this:
waveform_phi_0

The script first slices a CFD solution with several cylinders at different radial distances away from the X-axis. Then the cylinder is sliced with a plane at a few different angles to get slices that run in the X-direction for a constant Y and Z. I repeat this for a few different angles around the cylinder.

The code has worked for hundreds of cases and then failed on this one solution and I can’t figure out what caused it. Has anyone experienced anything similar before with slicing slices?

What it should look like:

Failed:

Turns out it was a corrupted solution .vtu file and some bad luck. The flow block is generated on an HPC system that just happened to time out the solution generation process halfway through and somehow the block was still ‘readable’. Regenerating the flow solution fixed the issue.