I am facing the same issue since yesterday. I have an ultimaker 1 and my problem started to appear after i drilled up the nozzle hole to 1mm. I think the G-Code is not he issue since the printer stopped at diffrent spots and hieghts when repeating a print with the same code.
What i observed today is that the printer seems to have powerloss for half a second and so loses all his tasks.
It came in my mind that maybe the Powre supply (230 to 12 or 24 DC) has an issue when running to warm. Did anybody tried with a new powersupply. I just pluged mine in as close as possibel on the power source a