I’ve looked in to this.
If I remember correctly, there’s some issue which prevents the bootloader from booting the kernel when your bootloader is updated.
It would be very difficult to diagnose why without direct UART access.
As a stop-gap, you could install this bootloader package https://collab.osmc.tv/s/vSCSD2aEuosKifC (using dpkg -i *.deb). It’s an empty package but will satisfy dependencies when upgrading, and the version has been set so high it will never be superseded.