Boot from NVME only works once

Hi
I’m having trouble with my Rock Pi 4c.
I followed all information that is available about NVME boot but what happens is the following:
I install Debian on the NVME with Etcher.
Then I boot from NVME, which works ok.
Then I try to reboot the Rock Pi 4C but it won’t boot up completely.
The error in the console I see is:
17.581548] cdn-dp fec00000.dp: Direct firmware load for rockchip/dptx.bin failed with error -2
[ 26.057473] random: nonblocking pool is initialized
[ 33.585559] cdn-dp fec00000.dp: Direct firmware load for rockchip/dptx.bin failed with error -2
[ 62.829378] nvme 0000:01:00.0: Timeout I/O 1 QID 0
[ 62.829870] nvme 0000:01:00.0: I/O 1 QID 0 timeout, reset controller
[ 62.933926] nvme 0000:01:00.0: Cancelling I/O 1 QID 0
[ 62.935396] nvme 0000:01:00.0: Device failed to resume

This happens every time!
My NVME is a Crucial P1 M.2 1TB. Is it not compatible? But why does it boot once and then not a second time?

Any ideas?
Thanks for your help.
Laci