Probably something changed with the boot configuration data, it's hard to go into specifics without knowing your exact setup but this should point you in the right direction...
BCDEdit Options Reference
learn.microsoft.com
You'll probably want to look at things like the timeout, the default entry, trying 'bcdedit /set {bootmgr} displaybootmenu yes'
e: FYI you don't actually need to use any bootmanager menus, like in the BIOS or the Windows one as you can set a default OS in your BIOS and create a shortcut to reboot into another OS, you only really need a boot menu if you want to choose on the fly.
E.g I have a shortcut with this command in the target box 'C:\Windows\System32\cmd.exe /c start bcdedit.exe /set {fwbootmgr} BOOTSEQUENCE {ccafcfa4-6e50-11ee-a77a-806e6f6e6963} && cmd /c start shutdown.exe /r /t 0' with the GUID (the part after BOOTSEQUENCE) taken from running 'Bcdedit /enum firmware'. That way i just have to click on the shortcut and it will reboot into the other OS and when i want to go back to my default OS i just reboot as that command only sets the boot order for the next reboot.
2nd e: To make that command clearer: 'C:\Windows\System32\cmd.exe /c start bcdedit.exe' open a command prompt and runs bcdedit.exe. '/set {fwbootmgr} BOOTSEQUENCE' tells bcdedit.exe to change the BIOS setting boot sequence the next time it reboots to a particular GUID. '&&' is the command to chain one command from another, so in other words run the first command and then run the second command. And the whole 'cmd /c start shutdown.exe /r /t 0' uses shutdown.exe to restart the PC right away. If you wanted to test it out you can do it all manually by opening a command prompt, get the GUID's of the various OS's by typing 'Bcdedit /enum firmware', then typing 'bcdedit.exe /set {fwbootmgr} BOOTSEQUENCE *insert desired GUID here including the {}*' and restarting manually.