I get similar behavior (EFI boot blocks run, boot loader 3.29 shows, but kernel fails to finish loading and reboots) on an Intel NUC DN2820FYKH using the latest snapshot (9/9) with install58.fs. I tried both bsd.rd and bsd for good measure. Installing via CSM works as expected.
Firing up the same installer in VirtualBox's EFI mode installs and runs beautifully, though, for whatever that's worth. Dmesg of the BIOS-booted NUC is below. Thanks. Brian OpenBSD 5.8-current (GENERIC.MP) #1364: Wed Sep 9 17:32:01 MDT 2015 dera...@amd64.openbsd.org:/usr/src/sys/arch/amd64/compile/GENERIC.MP real mem = 8473788416 (8081MB) avail mem = 8213020672 (7832MB) mpath0 at root scsibus0 at mpath0: 256 targets mainbus0 at root bios0 at mainbus0 acpi0 at bios0: rev 2 acpi0: sleep states S0 S3 S4 S5 acpi0: tables DSDT FACP APIC FPDT FIDT MCFG LPIT HPET SSDT SSDT SSDT UEFI acpi0: wakeup devices UAR5(S4) UAR8(S4) PS2K(S3) PS2M(S3) XHC1(S4) EHC1(S4) PXSX(S4) PXSX(S4) PXSX(S4) PXSX(S4) PWRB(S0) BRCM(S0) BRC3(S0) acpitimer0 at acpi0: 3579545 Hz, 24 bits acpimadt0 at acpi0 addr 0xfee00000: PC-AT compat cpu0 at mainbus0: apid 0 (boot processor) cpu0: Intel(R) Celeron(R) CPU N2820 @ 2.13GHz, 2133.82 MHz cpu0: FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,DS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE,SSE3,PCLMUL,DTES64,MWAIT,DS-CPL,VMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,SSE4.1,SSE4.2,MOVBE,POPCNT,DEADLINE,RDRAND,NXE,LONG,LAHF,3DNOWP,PERF,ITSC,SMEP,ERMS,SENSOR,ARAT cpu0: 1MB 64b/line 16-way L2 cache cpu0: smt 0, core 0, package 0 mtrr: Pentium Pro MTRR support, 8 var ranges, 88 fixed ranges cpu0: apic clock running at 133MHz cpu0: mwait min=64, max=64, C-substates=0.2.0.0.0.0.3.3, IBE cpu1 at mainbus0: apid 2 (application processor) cpu1: Intel(R) Celeron(R) CPU N2820 @ 2.13GHz, 2133.34 MHz cpu1: FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,DS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE,SSE3,PCLMUL,DTES64,MWAIT,DS-CPL,VMX,EST,TM2,SSSE3,CX16,xTPR,PDCM,SSE4.1,SSE4.2,MOVBE,POPCNT,DEADLINE,RDRAND,NXE,LONG,LAHF,3DNOWP,PERF,ITSC,SMEP,ERMS,SENSOR,ARAT cpu1: 1MB 64b/line 16-way L2 cache cpu1: smt 0, core 1, package 0 ioapic0 at mainbus0: apid 1 pa 0xfec00000, version 20, 87 pins acpimcfg0 at acpi0 addr 0xe0000000, bus 0-255 acpihpet0 at acpi0: 14318179 Hz acpiprt0 at acpi0: bus 0 (PCI0) acpiprt1 at acpi0: bus 1 (RP01) acpiprt2 at acpi0: bus 2 (RP02) acpiprt3 at acpi0: bus 3 (RP03) acpiprt4 at acpi0: bus 4 (RP04) acpiec0 at acpi0: not present acpicpu0 at acpi0: C1(1000@1 mwait.1), PSS acpicpu1 at acpi0: C1(1000@1 mwait.1), PSS acpipwrres0 at acpi0: PLPE acpipwrres1 at acpi0: PLPE acpipwrres2 at acpi0: USBC, resource for EHC1, OTG1 acpipwrres3 at acpi0: CLK0, resource for CAM1 acpipwrres4 at acpi0: CLK1, resource for CAM0, CAM2 acpibat0 at acpi0: BAT0 not present acpibat1 at acpi0: BAT1 not present acpibat2 at acpi0: BAT2 not present acpibtn0 at acpi0: PWRB acpibtn1 at acpi0: SLPB acpibtn2 at acpi0: LID0 acpivideo0 at acpi0: GFX0 cpu0: Enhanced SpeedStep 2133 MHz: speeds: 2129, 2128, 1995, 1862, 1729, 1596, 1463, 1330, 1197, 1064, 931, 798, 665, 532 MHz pci0 at mainbus0 bus 0 pchb0 at pci0 dev 0 function 0 "Intel Bay Trail Host" rev 0x0c vga1 at pci0 dev 2 function 0 "Intel Bay Trail Video" rev 0x0c intagp at vga1 not configured wsdisplay0 at vga1 mux 1: console (80x25, vt100 emulation) wsdisplay0: screen 1-5 added (80x25, vt100 emulation) ahci0 at pci0 dev 19 function 0 "Intel Bay Trail AHCI" rev 0x0c: msi, AHCI 1.3 ahci0: port 0: 3.0Gb/s scsibus1 at ahci0: 32 targets sd0 at scsibus1 targ 0 lun 0: <ATA, Crucial_CT240M50, MU05> SCSI3 0/direct fixed naa.500a07510c06ed9d sd0: 228936MB, 512 bytes/sector, 468862128 sectors, thin xhci0 at pci0 dev 20 function 0 "Intel Bay Trail xHCI" rev 0x0c: msi usb0 at xhci0: USB revision 3.0 uhub0 at usb0 "Intel xHCI root hub" rev 3.00/1.00 addr 1 "Intel Bay Trail TXE" rev 0x0c at pci0 dev 26 function 0 not configured ppb0 at pci0 dev 28 function 0 "Intel Bay Trail I2C" rev 0x0c: msi pci1 at ppb0 bus 1 ppb1 at pci0 dev 28 function 1 "Intel Bay Trail PCIE" rev 0x0c: msi pci2 at ppb1 bus 2 ppb2 at pci0 dev 28 function 2 "Intel Bay Trail PCIE" rev 0x0c: msi pci3 at ppb2 bus 3 re0 at pci3 dev 0 function 0 "Realtek 8168" rev 0x0c: RTL8168G/8111G (0x4c00), msi, address c0:3f:d5:63:f3:5a rgephy0 at re0 phy 7: RTL8251 PHY, rev. 0 ppb3 at pci0 dev 28 function 3 "Intel Bay Trail PCIE" rev 0x0c: msi pci4 at ppb3 bus 4 pcib0 at pci0 dev 31 function 0 "Intel Bay Trail LPC" rev 0x0c ichiic0 at pci0 dev 31 function 3 "Intel Bay Trail SMBus" rev 0x0c: apic 1 int 18 iic0 at ichiic0 iic0: addr 0x18 00=00 01=00 02=00 03=00 04=00 05=c2 06=1b 07=0a 08=00 09=00 0a=00 0b=00 0c=00 0d=00 0e=00 0f=00 words 00=007f 01=0000 02=0000 03=0000 04=0000 05=c27c 06=1b09 07=0a01 spdmem0 at iic0 addr 0x50: 8GB DDR3 SDRAM PC3-12800 SO-DIMM with thermal sensor isa0 at pcib0 isadma0 at isa0 com0 at isa0 port 0x3f8/8 irq 4: ns16550a, 16 byte fifo pckbc0 at isa0 port 0x60/5 irq 1 irq 12 pckbd0 at pckbc0 (kbd slot) wskbd0 at pckbd0: console keyboard, using wsdisplay0 pcppi0 at isa0 port 0x61 spkr0 at pcppi0 uhidev0 at uhub0 port 1 configuration 1 interface 0 " USB Keyboard" rev 1.10/3.10 addr 2 uhidev0: iclass 3/1 ukbd0 at uhidev0: 8 variable keys, 6 key codes wskbd1 at ukbd0 mux 1 wskbd1: connecting to wsdisplay0 uhidev1 at uhub0 port 1 configuration 1 interface 1 " USB Keyboard" rev 1.10/3.10 addr 2 uhidev1: iclass 3/0, 2 report ids uhid0 at uhidev1 reportid 1: input=1, output=0, feature=0 uhid1 at uhidev1 reportid 2: input=3, output=0, feature=0 umass0 at uhub0 port 2 configuration 1 interface 0 "Memorex Mini" rev 2.00/1.00 addr 3 umass0: using SCSI over Bulk-Only scsibus2 at umass0: 2 targets, initiator 0 sd1 at scsibus2 targ 1 lun 0: <Memorex, Mini, PMAP> SCSI4 0/direct removable serial.071807234ACEA30ACB22 sd1: 29560MB, 512 bytes/sector, 60538880 sectors uhidev2 at uhub0 port 3 configuration 1 interface 0 "Microsoft Microsoft 3-Button Mouse with IntelliEye(TM)" rev 1.10/3.00 addr 4 uhidev2: iclass 3/1 ums0 at uhidev2: 3 buttons, Z dir wsmouse0 at ums0 mux 0 vscsi0 at root scsibus3 at vscsi0: 256 targets softraid0 at root scsibus4 at softraid0: 256 targets root on sd0a (95519776ecf3f8f8.a) swap on sd0b dump on sd0b