We finally identified that the recording issues can be solved if you update the firmware of the DJ mixer you use with DJM-REC.
The issue: Recording or live streaming via a connection with a mixer may stop unexpectedly.
Please download your mixer's firmware from the links below and update the firmware to solve the DJM-REC issues.
DJM-900NXS2: Firmware Update Guide
DJM-450: Firmware Update Guide
DJM-750MK2: Firmware Update Guide
DJM-TOUR1: Firmware Update Guide