I took a look in the EFI entries of the NVRAM.
BootCurrent: 0006
Timeout: 1 seconds
BootOrder: 0006,0005,0001,0002,0003,0004,0000
Boot0000* Diagnostic Program FvVol(5c60f367-a505-419a-859e-2a4ff6ca6fe5)/FvFile(085e8cc2-8ec9-4666-bd2a-49d481e95fa7)
Boot0001* UEFI: PXE IP4 Realtek PCIe GBE Family Controller PciRoot(0x0)/Pci(0x14,0x0)/Pci(0x0,0x0)/Pci(0x5,0x0)/Pci(0x0,0x0)/MAC(0030591b9ad1,0)/IPv4(0.0.0.00.0.0.0,0,0)..BO
Boot0002* UEFI: PXE IP6 Realtek PCIe GBE Family Controller PciRoot(0x0)/Pci(0x14,0x0)/Pci(0x0,0x0)/Pci(0x5,0x0)/Pci(0x0,0x0)/MAC(0030591b9ad1,0)/IPv6([::]:<->[::]:,0,0)..BO
Boot0003* UEFI: PXE IP4 Intel(R) I210 Gigabit Network Connection PciRoot(0x0)/Pci(0x14,0x0)/Pci(0x0,0x0)/Pci(0x7,0x0)/Pci(0x0,0x0)/MAC(00305914304d,1)/IPv4(0.0.0.00.0.0.0,0,0)..BO
Boot0004* UEFI: PXE IP6 Intel(R) I210 Gigabit Network Connection PciRoot(0x0)/Pci(0x14,0x0)/Pci(0x0,0x0)/Pci(0x7,0x0)/Pci(0x0,0x0)/MAC(00305914304d,1)/IPv6([::]:<->[::]:,0,0)..BO
Boot0005* UEFI OS HD(1,GPT,acdf3a2f-43cc-44eb-8237-31711b75e4c9,0x4000,0x100000)/File(\EFI\BOOT\BOOTX64.EFI)..BO
Boot0006* ubuntu HD(1,GPT,acdf3a2f-43cc-44eb-8237-31711b75e4c9,0x4000,0x100000)/File(\EFI\UBUNTU\SHIMX64.EFI)
I changed the BootOrder to 0005,0006,0001,0002,0003,0004,0000. After restart the system “heals” itself.
BootCurrent: 0007
Timeout: 1 seconds
BootOrder: 0007,0005,0001,0002,0003,0004,0000
Boot0000* Diagnostic Program FvVol(5c60f367-a505-419a-859e-2a4ff6ca6fe5)/FvFile(085e8cc2-8ec9-4666-bd2a-49d481e95fa7)
Boot0001* UEFI: PXE IP4 Realtek PCIe GBE Family Controller PciRoot(0x0)/Pci(0x14,0x0)/Pci(0x0,0x0)/Pci(0x5,0x0)/Pci(0x0,0x0)/MAC(0030591b9ad1,0)/IPv4(0.0.0.00.0.0.0,0,0)..BO
Boot0002* UEFI: PXE IP6 Realtek PCIe GBE Family Controller PciRoot(0x0)/Pci(0x14,0x0)/Pci(0x0,0x0)/Pci(0x5,0x0)/Pci(0x0,0x0)/MAC(0030591b9ad1,0)/IPv6([::]:<->[::]:,0,0)..BO
Boot0003* UEFI: PXE IP4 Intel(R) I210 Gigabit Network Connection PciRoot(0x0)/Pci(0x14,0x0)/Pci(0x0,0x0)/Pci(0x7,0x0)/Pci(0x0,0x0)/MAC(00305914304d,1)/IPv4(0.0.0.00.0.0.0,0,0)..BO
Boot0004* UEFI: PXE IP6 Intel(R) I210 Gigabit Network Connection PciRoot(0x0)/Pci(0x14,0x0)/Pci(0x0,0x0)/Pci(0x7,0x0)/Pci(0x0,0x0)/MAC(00305914304d,1)/IPv6([::]:<->[::]:,0,0)..BO
Boot0005* UEFI OS HD(1,GPT,acdf3a2f-43cc-44eb-8237-31711b75e4c9,0x4000,0x100000)/File(\EFI\BOOT\BOOTX64.EFI)..BO
Boot0007* ubuntu HD(1,GPT,acdf3a2f-43cc-44eb-8237-31711b75e4c9,0x4000,0x100000)/File(\EFI\UBUNTU\SHIMX64.EFI)
Maybe I should delete the entry “ubuntu”!?