Windows stuck in bootloader when caddy is installed

There may be information in the logs.
When available please run and post a beta log collector zip into this thread.

Place the computer in clean boot this will be maintained until it is modified.
Evaluate the caddy in clean boot.:

Perform a Clean Boot in Windows 10 to Troubleshoot Software Conflicts

Caledon Ken said:

Check BIOS for FAST Boot. Disable. I would also disable Secure boot as part of test. Secure boot does not mean boot from SSD.

There is no option for fast boot. If I turn on Legacy Boot and disable Secure Boot, it will still be stuck in bootloader.

Maybe if you list the following details somebody might be able to help you:

Does SSD have MBR partitions or GPT partitions ? ( You said you rebuilt MBR of SSD)
Does Caddy Drive have MBR or GPT partitions ?
Does Bios/UEFI give list of bootable attached devices?

UPDATE: I turned on Legacy again with keeping my SSD boot priority first. Now I see a blank screen after the boot loader with just a cursor. Nothing else.

SSD is GPT. I think the caddy is MBR. I can see both drives in the BIOS menu.

Caledon Ken said:

What model is this. Looking at specs this device is new enough to have Fast Boot, might be named something different.

When you are shutting down Windows to make this change are you holding shift down and clicking Shutdown to bypass Windows Fast Startup?

It's HP ac-154ne. It has a shitty bios. Cannot see fast boot on the boot options.

No, I just do a normal shutdown.