Grub does not load ubuntu at boot

I have an HP EliteBook with a 128 GB SSD drive (/dev/sdb) and a 1 TB disk (/dev/sda). /dev/sda also has a windows 10 recovery partition which is used to load windows. I have left this partition alone and installed ubuntu 19.10 as follows:

/home on /dev/sda6
/boot on /dev/sdb2
/ on /dev/sdb5

Partitions look as follows:

sda:
/dev/sda1 EFI
/dev/sda2 Microsoft Reserved
/dev/sda3 Basic data
/dev/sda6 /home ******created by me from free space*******
/dev/sda4 MS windows recovery
/dev/sda5 basic data (system)

sdb (all created by me):

/dev/sdb1 EFI mounted at /boot/efi
/dev/sdb2 ext4 mounted at /boot
/dev/sdb3 ext4 mounted at /tmp
/dev/sdb4 swap
/dev/sdb5 ext4 mounted at /

After install, the system does not:

1. boot to Ubuntu (which is the only operational system - windows is just meant to be used for recovery and I have not used it)
2. may show a grub screen - on typing exit it goes into windows recovery

I tried boot-repair after which powering on or rebooting simply leads to the windows recovery screen

Previously I had installed ubuntu 19.04 on the same system without a problem.

But after doing a clean install of 19.10, the above problems have started

Now the only way I can boot into Ubuntu is by repeatedly pressing F9/F10 and going into the boot menu and choosing ubuntu.

What could be wrong?

Will be very difficult to use the system at this rate.

Any help or pointers are appreciated

Thanks in advance

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: grub-efi-amd64 2.04-1ubuntu12
ProcVersionSignature: Ubuntu 5.3.0-22.24-generic 5.3.7
Uname: Linux 5.3.0-22-generic x86_64
ApportVersion: 2.20.11-0ubuntu8.2
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Wed Nov 13 15:01:47 2019
InstallationDate: Installed on 2019-11-12 (1 days ago)
InstallationMedia: Ubuntu 19.10 "Eoan Ermine" - Release amd64 (20191017)
SourcePackage: grub2
UpgradeStatus: No upgrade log present (probably fresh install)