Replacing the file makes no difference if the error has already occurred. Just tried it out.
It is visual only, some kernel thread waits for an answer from a kernel module (actually it waits until another kernel module queries the GPU firmware, as far as I understand), which is not loaded by default on DietPi. It is interpreted as if it would cause CPU load while waiting, but actually it is not, hence this is visual only.
The related upstream developer could replicate it and wrote he will try to fix it, but no further message since a month: Making sure you're not a bot!
If someone wants to narrow down which modules cause this, comment blacklists in those two files:
/etc/modprobe.d/dietpi-disable_rpi_codec.conf/etc/modprobe.d/dietpi-disable_rpi_camera.conf
They are related to the RPi codec and camera settings in `dietpi-config`. One could also enable the codecs there, but enabling the camera implies the legacy camera driver, which is not wanted. I really need to migrate this to use the modern one …
If unblocking/loading those modules does not help, try to set the GPU memory to default value 76 MiB, which is needed for some of the GPU features to work. With below 32 MiB, a cut-down firmware is loaded, which makes some of the GPU features unusable. I don’t believe those are responsible for the newly handing thread, but who knows.
Exact the same situtation in my case. Only difference i use an Raspi 3B.