UEFI is tricky, and the bootloader is only at the end of the chain. But I insist that bootx64.efi 555008 is erratic. Recalbox has it also on their distribution image, I will come later to this. 🙂
Now concerning X45, its the same family and it should behave the same way.
One thing that could be important also, Batocera 5.18 is based on kernel 4.17, Batocera 5.19 on kernel 4.18. (Recalbox distr. on kernel 4.8.....)
Lets first try with the X45. So, important, if you dont did it already, upgrade the bios to 0.14. You find the download in the F.A.Q. on Beelink's website. And better not to delete Windows10 on SSD, because you will need it to upgrade bios. I compressed W10 to about 30GB (after update to 1803) and use the staying 90GB for the share folder, this works best. If you intend to upgrade to bigger SSD (also risky) better to save the system before with a tool like "Drive Snapshot".
Now, with the new bios 0.14, in case of OS on USB, some things to change inside
ADVANCED - USB Confiruration - Legacy USB Support = Enabled
ADVANCED - USB Confiruration - USB Mass Storage Support = Enabled
ADVANCED - Mass Storage Device - Generic-SD/MMC = Auto
CHIPSET - South Cluster Configuration - USB Configuration - XHCI Preboot Driver = Enabled
CHIPSET - South Cluster Configuration - USB Configuration - XHCI Mode = Enabled
SECURITY - Security Boot - Secure Boot = Disabled
SECURITY - Security Boot - Secure Boot Customization = Custom
BOOT - Boot Option # 1 = UEFI Generic SD/MMC....
BOOT - Boot Option # 2 = Windows Boot Manager
SAVE & Exit
That is one part. If you install Batocera on SSD, emmc, there could be another problem.
Because MBR is too old to communicate with UEFI, so you should use GPT instead and this is also the partition table used by BeeLink at delivry.
There exist some software, to swap it without formating the disk. The only free that I know is "Minitool Partition Wizard" and only last trial version. There may be still other problems, but for X45 it should work.
As I told before, I also arrived with the x86 - 64 from Recalbox. But after, keyboard use on usb is impossible and very big lags in game execution. I dont really arrived to some good result. Even my mame games that are working on PI3B- showed no live. This may also be the 4.8 kernel use.
With Batocera x86 - 64 it was much more strait forward and yesterday evening (the X55 is planned for my shooting gallery in bedroom 😉 ), "Carnevil" was working perfect and quick on the X55. With the PI3B-, I had just a steady picture. I am looking also for Time Crisis and the other and will tell about my experience.