Have you updated your pedal? There is new software available that fixes a bug we found after we shipped the first batch of Blackholes where something similar could happen on some units. You'll need to plug in the USB to a computer and use Eventide Device Manager to update to the newest version (1.0.1).
Are you using the included power supply? This could also happen with a power supply that isn't providing enough current to properly feed your Blackhole.
I just bought a new Blackhole pedal (February 20210), and after being powered on for a while (an hour or so), the pedal acts like it’s in bypass. I hear my input but with no effect applied. Power-cycling resolves the issue, but the pedal continues to “turn off” after a while. I haven’t changed any of the presets or done anything else but use the pedal at its default settings.
Thanks for your reply! No, I haven’t updated the firmware yet. I just bought it (March 2021) so I assumed it was recent stock. I was using a new Trutone 1Spot 9V PSU and also tried a premium Dunlop 9V power supply (i.e., larger PSU with thicker cables) with the same results. Will try the firmware upgrade next and report back. Thanks!