Same problem with me.....
My Windows 10 guest(s) have same problem unexpected reboot shutdown...
My configuration is same...
Linux Mint 20.1 Cinamon
Kernel 5.8.0-44-generic
11th Gen I5-1135g7
Graph: İntel Xiris and Nvdia mx 450
Lenovo e14 gen 2 intel
32 Gb Ram
00:05:28.724160 GIM: HyperV: Guest indicates a fatal condition! P0=0x1e P1=0xffffffff80000002 P2=0xfffff80398286d11 P3=0xf45 P4=0x2
00:05:28.724321 GIMHv: BugCheck 1e {ffffffff80000002, fffff80398286d11, f45, 2}
00:05:28.724322 KMODE_EXCEPTION_NOT_HANDLED
00:05:28.724322 P1: ffffffff80000002 - exception code - STATUS_DATATYPE_MISALIGNMENT
SAME WITH TEST VERSION
00:00:00.857515 VirtualBox VM 6.1.19 r142995 linux.amd64 (Mar 2 2021 13:22:09) release log
00:00:00.857517 Log opened 2021-03-11T16:02:36.035931000Z
00:00:00.857517 Build Type: release
00:00:00.857519 OS Product: Linux
00:00:00.857520 OS Release: 5.8.0-44-generic
00:00:00.857520 OS Version: #50~20.04.1-Ubuntu SMP Wed Feb 10 21:07:30 UTC 2021
00:00:00.857542 DMI Product Name: 20TBS08500
00:00:00.857546 DMI Product Version: ThinkPad E14 Gen 2
00:00:00.857551 Firmware type: UEFI
00:00:00.857828 Secure Boot: Disabled
00:00:00.857860 Host RAM: 31814MB (31.0GB) total, 29247MB (28.5GB) available
00:00:00.857863 Executable: /opt/VirtualBox/VirtualBoxVM
00:00:00.857863 Process ID: 12098
00:00:00.857863 Package type: LINUX_64BITS_GENERIC
00:04:21.137131 GIM: HyperV: Guest indicates a fatal condition! P0=0x1e P1=0xffffffff80000002 P2=0xfffff80356a9810c P3=0xffff870e1c696ade P4=0x7010008004002001
00:04:21.137323 GIMHv: BugCheck 1e {ffffffff80000002, fffff80356a9810c, ffff870e1c696ade, 7010008004002001}
00:04:21.137324 KMODE_EXCEPTION_NOT_HANDLED
00:04:21.137324 P1: ffffffff80000002 - exception code - STATUS_DATATYPE_MISALIGNMENT
00:04:21.137324 P2: fffff80356a9810c - EIP/RIP
00:04:21.137324 P3: ffff870e1c696ade - Xcpt param #0
00:04:21.137325 P4: 7010008004002001 - Xcpt param #1
00:04:24.955894 VMMDev: vmmDevHeartbeatFlatlinedTimer: Guest seems to be unresponsive. Last heartbeat received 4 seconds ago
00:04:25.971428 AHCI#0: Reset the HBA
00:04:25.971445 VD#0: Cancelling all active requests
00:04:25.972802 AHCI#0: Port 0 reset
00:04:25.973821 VD#0: Cancelling all active requests
00:04:30.882633 GUI: UIMachineView::sltPerformGuestResize: Sending guest size-hint to screen 0 as 1264x1047 if necessary
00:04:30.887716 VMMDev: SetVideoModeHint: Got a video mode hint (1264x1047x32)@(0x0),(1;0) at 0
00:04:30.891687 GUI: UIMediumEnumerator: Medium-enumeration finished!
00:04:32.807365 GUI: UIMachineView::sltPerformGuestResize: Sending guest size-hint to screen 0 as 1535x777 if necessary
00:04:42.733946 VMMDev: Guest Log: VBoxGuest: BugCheck! P0=0x1e P1=0xffffffff80000002 P2=0xfffff80356a9810c P3=0xffff870e1c696ade P4=0x7010008004002001
00:04:42.734205 GIM: HyperV: Reset initiated through MSR
00:04:42.736540 Changing the VM state from 'RUNNING' to 'RESETTING'
00:04:42.737491 GIM: HyperV: Resetting MMIO2 regions and MSRs
00:04:42.737552 PIT: mode=3 count=0x10000 (65536) - 18.20 Hz (ch=0)
00:04:42.738271 GUI: UISession::sltAdditionsChange: GA state really changed, notifying listeners
00:04:42.738323 GUI: UIMachineViewNormal::adjustGuestScreenSize: Adjust guest-screen size if necessary
00:04:42.738370 GUI: UISession::sltAdditionsChange: GA state change event came, notifying listeners
00:04:42.738377 GUI: UIMachineLogicNormal::sltCheckForRequestedVisualStateType: Requested-state=0, Machine-state=5
00:04:42.738401 GUI: UISession::sltAdditionsChange: GA state change event came, notifying listeners
00:04:42.738405 GUI: UIMachineLogicNormal::sltCheckForRequestedVisualStateType: Requested-state=0, Machine-state=5