How to remove "BOOT MISMATCH!" message before picker?

Hello, I'm pretty new to this but I (somehow) managed to get macOS Sierra working on my i3-380M 8GB 128GB SSD with only Legacy boot laptop. My question is how can I remove the "BOOT MISMATCH!" message before the OpenCore picker shows up. Everything works great besides that message, it sometimes annoy me, and affect the boot time because it means "Bootstrap partition signature identification failed" and takes 3 second to look up "EFI/OC/OpenCore.efi" on any partition. I've done some research on my own and I haven't found any useful information, most of them have the error message come with other messages that helps them fix it, but mine is just "BOOT MISMATCH!" then continue. I really appreciate any help with this.

submitted by /u/NDHoangMinh
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