Ah I think I know of another way it can go wrong, I had not thought of this before.
I took out my jars out if the PC pretty quickly this time to speed up the cool down. When cooling down it can suck in air and spores from outside because of pressure differences. At that point I only have one layer of micropore on there to help the sterilization process. After inoculation I put a second layer on there.
Big chance some spores get sucked in, in those few hours of cooling down, or get stuck on that first layer of micropore tape, which then would easily get through after I put on a second layer.
Makes more sense than the cardboard box I mentioned earlier..
I have some points for improvement I see: Let the jars cool down in my PC and sterilize longer.
It's hard to point out where these things go wrong exactly, many factors that come into play. I had not even thought of SHIPs being able to cause trouble..
Edited by RutgerHauer, 05 February 2020 - 01:36 PM.