Same problem on Dell Inspiron 3593 with dual boot Windows 10 and Ubuntu 18.04.
As Johann Gail writes, this was previously working without problem until a few weeks ago.
I have not tried the tpm fix.
I have tried changing boot order, enabling/disabling secure boot - neither of these appear to solve the problem.
Typing "reboot" at the grub prompt sometimes works immediately, other times I need to reboot again before booting successfully.
Same problem on Dell Inspiron 3593 with dual boot Windows 10 and Ubuntu 18.04.
As Johann Gail writes, this was previously working without problem until a few weeks ago.
I have not tried the tpm fix.
I have tried changing boot order, enabling/disabling secure boot - neither of these appear to solve the problem.
Typing "reboot" at the grub prompt sometimes works immediately, other times I need to reboot again before booting successfully.