Obviously there is a problem with TTY devices with the new kernel. The HAT registers itself as TTY as well. They've changed something at the registration process and this might cause problems on some systems. The problem definitely exists on the Pi 3 and Pi 3+. We didn't face any issues with the Pi 4. However, the theoretically the problem might be on the Pi 4 as well, if the system uses additional TTY devices.
A solution is already in testing stage and we might publish soon if successfull.
A solution is already in testing stage and we might publish soon if successfull.