Thanks for your reply.
The issue is that I cannot recreate the scenario which causes the outputs DIO 30 & 31 to fail in shop.
I tried running the outputs at a rate of 500hz and everything functions properly.
The issue which I reported only occurs at an install offsite, and very randomly.
I am suspecting the issue may be related to the wiring, or possibly environmental (noise, voltage...).
Since we moved the I/O from DIO 30 / 31 to other outputs we have not encountered any issues.
I will continue researching the issue and let you know if / when a resolution is discovered.