[Moto G5 Plus ROMs, Kernels, Recoveries, & Other De] NeoPolus:
Done (cleaning cache+dalvik before and after flashing the kernel), but the problem persists.

I also tried (with no luck):

Setting "noop" as the external IO excheduler (apply on bot instantly) and reboot.

Removing the second SIM card.

It seems vold/StorageManagerService is crashing somehow (couldn't find anything else useful on the logs):

04-08 09:04:50.067 root 485 485 V vold : /system/bin/sgdisk

04-08 09:04:50.068 root 485 485 V vold : --android-dump

04-08 09:04:50.068 root 485 485 V vold : /dev/block/vold/disk:179,64

04-08 09:04:50.361 root 485 485 V vold : DISK mbr

04-08 09:04:50.361 root 485 485 V vold :

04-08 09:04:50.361 root 485 485 V vold : PART 1 7

04-08 09:04:50.361 root 485 485 V vold :

04-08 09:04:50.365 root 485 491 V vold : /system/bin/blkid

04-08 09:04:50.365 root 485 491 V vold : -c

04-08 09:04:50.365 root 485 491 V vold : /dev/null

04-08 09:04:50.365 root 485 491 V vold : -s

04-08 09:04:50.365 root 485 491 V vold : TYPE

04-08 09:04:50.365 root 485 491 V vold : -s

04-08 09:04:50.365 root 485 491 V vold : UUID

04-08 09:04:50.365 root 485 491 V vold : -s

04-08 09:04:50.365 root 485 491 V vold : LABEL

04-08 09:04:50.365 root 485 491 V vold : /dev/block/vold/public:179,65

04-08 09:04:50.642 root 485 491 V vold : /dev/block/vold/public:179,65: LABEL="disk" UUID="B530-CAB8" TYPE="exfat"

04-08 09:04:50.642 root 485 491 V vold :

04-08 09:04:50.645 root 485 491 V vold : /system/bin/fsck.exfat

04-08 09:04:50.645 root 485 491 V vold : /dev/block/vold/public:179,65

04-08 09:04:58.291 root 485 491 I vold : Check OK

04-08 09:04:58.295 root 485 491 E vold : Mount failed; attempting read-only: I/O error

04-08 09:04:58.296 root 485 491 E vold : public:179,65 failed to mount /dev/block/vold/public:179,65: I/O error

04-08 09:04:58.296 1000 702 1146 E StorageManagerService:

04-08 09:04:58.296 1000 702 1146 E StorageManagerService: android.os.ServiceSpecificException: (code -5)

04-08 09:04:58.296 1000 702 1146 E StorageManagerService:	at android.os.Parcel.createException(Parcel.java:1964)

04-08 09:04:58.296 1000 702 1146 E StorageManagerService:	at android.os.Parcel.readException(Parcel.java:1918)

04-08 09:04:58.296 1000 702 1146 E StorageManagerService:	at android.os.Parcel.readException(Parcel.java:1868)

04-08 09:04:58.296 1000 702 1146 E StorageManagerService:	at android.os.IVold$Stub$Proxy.mount(IVold.java:773)

04-08 09:04:58.296 1000 702 1146 E StorageManagerService:	at com.android.server.StorageManagerService$StorageManagerServiceHandler.handleMessage(StorageManagerService.java:623)

04-08 09:04:58.296 1000 702 1146 E StorageManagerService:	at android.os.Handler.dispatchMessage(Handler.java:106)

04-08 09:04:58.296 1000 702 1146 E StorageManagerService:	at android.os.Looper.loop(Looper.java:193)

04-08 09:04:58.296 1000 702 1146 E StorageManagerService:	at android.os.HandlerThread.run(HandlerThread.java:65)

04-08 09:04:58.297 1000 702 1146 D StorageManagerService: Volume public:179,65 broadcasting checking to UserHandle{0}

04-08 09:04:58.298 1000 702 1146 D StorageManagerService: Volume public:179,65 broadcasting unmountable to UserHandle{0}

I'm back to default kernel and the problem is gone.