dual boot - boot loader not always loaded

Hello!

I got a problem with my Windows 10 / Windows 7 dual boot system.

The boot loader does not come up every time. It depends on what I did before.
Shut down Windows 10 -> boot loader does not show up on next boot and Windows 10 boots up.
Reboot Windows 10 -> boot loader shows up and I can choose which OS to start.
Shut down Windows 7 -> boot loader shows up and I can choose which OS to start.
Reboot Windows 7 -> boot loader shows up and I can choose which OS to start.

Of course I want the boot loader to show up every time.

What I did:
Windows 10 was preinstalled. Then I reduced the partition size of Windows 10 and created another primary partition for Windows 7. Windows 7 was then installed in this new partition.

Does anyone know what causes this behavior?

Thanks in advance

Turn off fast startup in Windows 10:
https://www.tenforums.com/tutorials/...dows-10-a.html

Many Thanks - That did it.
It can be very easy sometimes.

Problem solved

Yep.... just need to know someone who has the easy answer