I have noticed that each time I update to the latest Insider Preview Build, a change takes place in my boot order. I have a Crucial SSD with Windows installed, and a Toshiba 1Tb HDD as secondary drive. After an update, the computer will try to boot from the Toshiba. I have to go into the bios and change the boot order, then it will work fine until the next update.
I do not know if this is an issue with the mobo or with the Preview builds. I am running an Intel Pentium G4440 on an Asrock ITX mobo.
Yes I had that too but only for one release. Each time I rebooted it dropped to BIOS, I clicked close and everything booted perfectly, I didn't need to alter the boot drives. Now on 17704.rs_prerelease.180623-1611 and all seems happy again.