Findings:

It seems that a voltage dip or voltage irregularity causes corrupt data to be written to the Codex card triggering a "Recording Stopped unexpectedly (#138)" error. Once a card has become corrupted, the camera's Media → Format does not clear a root level corruption and the card will continue to trigger error #138. Some things that have triggered it:

• Ejecting and quickly reinserting a physically hot card.
• Unplugging 24v power source during a take and the camera switches to a 14v GoldMount
• Recording higher FPS seems to be more likely to trigger the error.
• Once a card has been involved with a Error 138 incident, it is highly likely that it will have an error again even after being formatted inside the camera.
• Although the above issues were present when the error occurred, it is not consistent. Unplugging the 24v source will trigger the error one time but not the next. This inconsistency makes it difficult to pinpoint the causation.

It seems that formatting the Codex Card using the Codex Device Manager app on MacOS will 'reset' the card for a longer period of time before an error will occur.

Problem: While shooting a commercial in Los Angeles CA on 7/17/20, experienced the camera shutting down while recording.

Was shooting at 36fps in 4.5k ProRes4444. Recording Stopped unexpectedly (#138)

Discussion on Arri Forums: https://forum.arri.com/viewtopic.php?f=105&t=1343

The following are attempts to recreate the problem. Things I cannot recreate: Exterior temperature was around 85 degrees and very sunny. Also cannot create the scenes we were shooting. We were shooting around a pool with a lot of water movement.

Setup Alexa Mini LF 31396 Software 6.0.2.1 Revision 33511 FPGA (#8) 4584/6130 MVF Software 1.67 Lens Mount 1.22