I mean this appears to be a solid answer, we'll know once the OP has updated and tested this.What version DriveHub are you running? Beta firmware (2.0.8 and above) should resolve this issue.
I remember a YouTuber having this same issue, only it was during some of the license tests or missions. I think it was Jimmy Broadbent, but he was entering into whatever drive he was set up for, and similar to you, the ABS kept randomly flashing and the car would begin braking at random times or just all the time. IIRC he runs a mix of Fanatec and Heusinkfeld gear. I think for his a simple "turn it off and on again" fixed it, but I'm glad to see you hopefully found a resolution.UPDATE: New firmware for the DriveHub out. Running 2.08 Beta9. I just had my first complete sport race. Qualy'd 3rd, finished 6th (had an off). But hey, I'm in the mix now. Definitely think it was a hardware issue with the drivehub. Now I just need to remap my rearview mirror button.