Spanner has hit its mark. We have now released a beta version of the firmware (v 7.3.9) which further addresses the issue of missing log files:
1. It has a more robust response to USB errors, so it can recover from most USB problems and restart the log, and if it can't recover it will tell you (memory sticks can become flaky over time).
2. It has a small memory stick icon that appears in the bottom right corner of the screen while a log is being written. This provides reassurance that a log is being recorded.
The update can be downloaded from our beta page https://drive.google.com/open?id=1Voy1m ... o--Q-ud2cb
Please let us know how this goes for you. If you still have zero-byte log files after this we will have to start thinking about faulty circuitry in your roaster.