[Samsung Galaxy S7 Edge Questions and Answers] Yom:
Interesting... the dmesg log has these vold lines on it:

[20272.463905] [6: vold: 3169] [EXFAT] (mmcblk0p1[179:1]): trying to mount...

and then...

[20272.768912] [4: vold: 3169] vold: page allocation failure: order:6, mode:0x40d0
[20272.768930] [4: vold: 3169] CPU: 4 PID: 3169 Comm: vold Tainted: G W 3.18.14-8040641 #1
[20272.768942] [4: vold: 3169] Hardware name: Samsung UNIVERSAL8890 board based on EXYNOS8890 (DT)
[20272.768952] [4: vold: 3169] Call trace:
[20272.768974] [4: vold: 3169] [<ffffffc000129328>] dump_backtrace+0x0/0x10c
[20272.768987] [4: vold: 3169] [<ffffffc000129444>] show_stack+0x10/0x1c
[20272.769001] [4: vold: 3169] [<ffffffc000a4bdbc>] dump_stack+0x80/0xc4
[20272.769014] [4: vold: 3169] [<ffffffc0001e0374>] warn_alloc_failed+0x114/0x130
[20272.769027] [4: vold: 3169] [<ffffffc0001e367c>] __alloc_pages_nodemask+0x634/0x824
[20272.769074] [4: vold: 3169] [<ffffffc0001e3950>] alloc_kmem_pages+0x14/0x20
[20272.769091] [4: vold: 3169] [<ffffffc0001f8cbc>] kmalloc_order+0x10/0x58
[20272.769101] [4: vold: 3169] [<ffffffc0001f8d28>] kmalloc_order_trace+0x24/0xd0
[20272.769113] [4: vold: 3169] [<ffffffc00021e5cc>] __kmalloc+0x48/0x1e8
[20272.769126] [4: vold: 3169] [<ffffffc000314c10>] load_alloc_bitmap+0xd4/0x1a4
[20272.769135] [4: vold: 3169] [<ffffffc000315120>] ffsMountVol+0xf0/0x168
[20272.769145] [4: vold: 3169] [<ffffffc000317ea4>] FsMountVol+0x84/0xe4
[20272.769159] [4: vold: 3169] [<ffffffc00031bc44>] exfat_fill_super+0x120/0x2e8
[20272.769170] [4: vold: 3169] [<ffffffc00022914c>] mount_bdev+0x134/0x19c
[20272.769179] [4: vold: 3169] [<ffffffc00031b4e8>] exfat_fs_mount+0x10/0x1c
[20272.769187] [4: vold: 3169] [<ffffffc0002293f0>] mount_fs+0x78/0x174
[20272.769201] [4: vold: 3169] [<ffffffc00024231c>] vfs_kern_mount+0x64/0x11c
[20272.769210] [4: vold: 3169] [<ffffffc0002440b0>] do_mount+0x8b8/0x990
[20272.769219] [4: vold: 3169] [<ffffffc0002443d0>] SyS_mount+0x84/0xc0
[20272.769227] [4: vold: 3169] Mem-Info:
[20272.769234] [4: vold: 3169] Normal per-cpu:
[20272.769242] [4: vold: 3169] CPU 0: hi: 186, btch: 31 usd: 34
[20272.769250] [4: vold: 3169] CPU 1: hi: 186, btch: 31 usd: 31
[20272.769258] [4: vold: 3169] CPU 2: hi: 186, btch: 31 usd: 31
[20272.769266] [4: vold: 3169] CPU 3: hi: 186, btch: 31 usd: 0
[20272.769273] [4: vold: 3169] CPU 4: hi: 186, btch: 31 usd: 0
[20272.769281] [4: vold: 3169] CPU 5: hi: 186, btch: 31 usd: 68
[20272.769288] [4: vold: 3169] CPU 6: hi: 186, btch: 31 usd: 61
[20272.769296] [4: vold: 3169] CPU 7: hi: 186, btch: 31 usd: 50
[20272.769312] [4: vold: 3169] active_anon:116216 inactive_anon:124169 isolated_anon:9
[20272.769312] [4: vold: 3169] active_file:61863 inactive_file:34157 isolated_file:3
[20272.769312] [4: vold: 3169] unevictable:0 dirty:2 writeback:0 unstable:0
[20272.769312] [4: vold: 3169] free:53092 slab_reclaimable:15714 slab_unreclaimable:38098
[20272.769312] [4: vold: 3169] mapped:70099 shmem:5490 pagetables:29132 bounce:0
[20272.769312] [4: vold: 3169] free_cma:2903
[20272.769350] [4: vold: 3169] Normal free:212368kB min:7628kB low:47888kB high:49796kB active_anon:464864kB inactive_anon:496676kB active_file:247452kB inactive_file:136628kB unevictable:0kB isolated(anon):36kB isolated(file):12kB present:4165632kB managed:3648156kB mlocked:0kB dirty:8kB writeback:0kB mapped:280396kB shmem:21960kB slab_reclaimable:62856kB slab_unreclaimable:152392kB kernel_stack:54144kB pagetables:116528kB unstable:0kB bounce:0kB free_cma:11612kB writeback_tmp:0kB pages_scanned:0 all_unreclaimable? no
[20272.769358] [4: vold: 3169] lowmem_reserve[]: 0 0
[20272.769367] [4: vold: 3169] Normal: 23471*4kB (UEMC) 9001*8kB (UEMC) 1918*16kB (UEMRC) 141*32kB (UEMC) 12*64kB (MC) 7*128kB (C) 6*256kB (C) 5*512kB (C) 3*1024kB (C) 1*2048kB (C) 0*4096kB = 211972kB
[20272.769407] [4: vold: 3169] 111582 total pagecache pages
[20272.769415] [4: vold: 3169] 10071 pages in swap cache
[20272.769423] [4: vold: 3169] Swap cache stats: add 19610306, delete 19600235, find 6738154/14578558
[20272.769431] [4: vold: 3169] Free swap = 32kB
[20272.769438] [4: vold: 3169] Total swap = 2097148kB
[20272.769445] [4: vold: 3169] 1041408 pages RAM
[20272.769452] [4: vold: 3169] 0 pages HighMem/MovableOnly
[20272.769459] [4: vold: 3169] 129369 pages reserved
[20272.769468] [4: vold: 3169] [EXFAT] FsMountVol failed
[20272.769478] [4: vold: 3169] [EXFAT] (mmcblk0p1[179:1]): failed to mount!

As for logcat...

05-27 09:37:17.624 2945 3169 I fsck.exfat: No errors
05-27 09:37:17.624 2945 3169 I fsck.exfat: end(ret:0, dev:/dev/block/vold/public:179,1)
05-27 09:37:17.624 2945 3169 V vold : public:179,1 check filesystem format: 1
05-27 09:37:17.624 2945 3169 V vold : stableName: D6DA-057C (id:public:179,1, mFsUuid:D6DA-057C)
05-27 09:37:17.634 2945 3169 V vold : exfat::Mount() /dev/block/vold/public:179,1 to /mnt/media_rw/D6DA-057C
05-27 09:37:17.634 2945 3169 V vold : mFsLabel : 64GBmSD, mFsUuid : D6DA-057C
05-27 09:37:18.514 2945 3169 E vold : public:179,1 failed to mount /dev/block/vold/public:179,1: I/O error
05-27 09:37:18.514 5428 5546 D VolumeInfo: VolumeInfo from Parcel: id public:179,1 ,type 0 ,disk DiskInfo{disk:179,0}:
05-27 09:37:18.514 5428 5546 D VolumeInfo: flags=SD size=63864569856 label=
05-27 09:37:18.514 5428 5546 D VolumeInfo: sysPath=/sys//devices/15740000.dwmmc2/mmc_host/mmc0/mmc0:e624/block/mmcblk0
05-27 09:37:18.514 5428 5546 D VolumeInfo:
05-27 09:37:18.514 8823 5310 D VolumeInfo: VolumeInfo from Parcel: id public:179,1 ,type 0 ,disk DiskInfo{disk:179,0}:
05-27 09:37:18.514 8823 5310 D VolumeInfo: flags=SD size=63864569856 label=
05-27 09:37:18.514 8823 5310 D VolumeInfo: sysPath=/sys//devices/15740000.dwmmc2/mmc_host/mmc0/mmc0:e624/block/mmcblk0
05-27 09:37:18.514 8823 5310 D VolumeInfo:
05-27 09:37:18.514 6388 16377 D VolumeInfo: VolumeInfo from Parcel: id public:179,1 ,type 0 ,disk DiskInfo{disk:179,0}:
05-27 09:37:18.514 6388 16377 D VolumeInfo: flags=SD size=63864569856 label=
05-27 09:37:18.514 6388 16377 D VolumeInfo: sysPath=/sys//devices/15740000.dwmmc2/mmc_host/mmc0/mmc0:e624/block/mmcblk0
05-27 09:37:18.514 6388 16377 D VolumeInfo:
05-27 09:37:18.514 6388 6388 D StorageNotification: Notifying about public volume: VolumeInfo{public:179,1}:
05-27 09:37:18.514 6388 6388 D StorageNotification: type=PUBLIC diskId=disk:179,0 partGuid=null mountFlags=VISIBLE
05-27 09:37:18.514 6388 6388 D StorageNotification: mountUserId=0 state=UNMOUNTABLE
05-27 09:37:18.514 6388 6388 D StorageNotification: fsType=exfat fsUuid=D6DA-057C fsLabel=64GBmSD
05-27 09:37:18.514 6388 6388 D StorageNotification: path=/storage/D6DA-057C internalPath=/mnt/media_rw/D6DA-057C
05-27 09:37:18.514 8823 8823 D MtpService: onStorageStateChanged /storage/D6DA-057C checking -> unmountable
05-27 09:37:18.524 18853 18853 E Sm : Error
05-27 09:37:18.524 18853 18853 E Sm : java.lang.IllegalStateException: command '30 volume mount public:179,1 2 0' failed with '400 30 Command failed'

Attaching the logs you requested, thank you for your help, sir.