I think you can choose which GPU that you want to use in the BIOS; you'll have to look.
IF not you will have to blacklist the onboard GPU.
Just open your /etc/modprobe.d/blacklist file and blacklist the onboard GPU by disabeling the driver for it.
This error that you are getting:
unexpectedly disconnected from boot status daemon
indicates one of 2 things. Either there is a problem with Plymouth or there is an issue having 2 different graphic cards.I do not have experience at manipulating Plymouth, sorry.
This error message is a Bug-
This might help. I'm not sure if Grub is the problem. I'm thinking that there is more likely conflict between the 2 graphic cards.
What is the output of this?
lspci | grep -i VGA