SDCard corrupted, wont format, slow to read - Android Q&A, Help & Troubleshooting

Ive been having nightmares with a 128 GB SDCard that had been going fine till I decided I wanted to format it as mixed. I did this using adb and my Marshmallow phone. At first it all went well but then I decided I wanted to tweak the mix and put a bit more as shared (rather than adopted), this time I was using a 7.1.2 ROM (and adb) and thats when the nightmares started.
I have managed a couple of times to reformat it so the phone will accept it but the thing seems very fragile. I just have to squint at it and suddenly - its corrupted.
So Im trying to work out if there is something wrong with it or if its a software issue - here is some logcat that may be relevant - captured while im trying to partition the card with:
Code:
adb shell sm partition disk:179,64 private
Could somebody help me understand what this log is telling us?
Code:
07-31 04:05:15.754 30095 30095 D AndroidRuntime: >>>>>> START com.android.internal.os.RuntimeInit uid 2000 <<<<<<
07-31 04:05:15.763 30095 30095 D AndroidRuntime: CheckJNI is OFF
07-31 04:05:15.825 30095 30095 D ICU : No timezone override file found: /data/misc/zoneinfo/current/icu/icu_tzdata.dat
07-31 04:05:15.873 30095 30095 I Radio-JNI: register_android_hardware_Radio DONE
07-31 04:05:15.902 30095 30095 D AndroidRuntime: Calling main entry com.android.commands.sm.Sm
07-31 04:05:15.905 1928 7704 D VoldConnector: SND -> {199 volume partition disk:179,64 private}
07-31 04:05:15.905 275 281 V vold : /system/bin/sgdisk
07-31 04:05:15.905 275 281 V vold : --zap-all
07-31 04:05:15.905 275 281 V vold : /dev/block/vold/disk:179,64
07-31 04:05:15.900 7704 7704 I Binder_B: type=1400 audit(0.0:1122): avc: denied { getopt } for scontext=u:r:system_server:s0 tcontext=u:r:init:s0 tclass=unix_dgram_socket permissive=1
07-31 04:05:15.900 7704 7704 I Binder_B: type=1400 audit(0.0:1123): avc: denied { write } for path="socket:[12111]" dev="sockfs" ino=12111 scontext=u:r:system_server:s0 tcontext=u:r:init:s0 tclass=unix_dgram_socket permissive=1
........
07-31 04:06:09.184 275 281 I sgdisk : Warning: The kernel is still using the old partition table.
07-31 04:06:09.184 275 281 I sgdisk : The new table will be used at the next reboot.
07-31 04:06:09.185 275 281 I sgdisk : GPT data structures destroyed! You may now partition the disk using fdisk or
07-31 04:06:09.185 275 281 I sgdisk : other utilities.
......
07-31 04:06:15.906 1928 7704 E NativeDaemonConnector.ResponseQueue: Timeout waiting for response
07-31 04:06:15.906 1928 7704 E VoldConnector: timed-out waiting for response to 199 volume partition disk:179,64 private
07-31 04:06:15.909 30095 30095 E Sm : Error
07-31 04:06:15.909 30095 30095 E Sm : java.lang.IllegalStateException: command '199 volume partition disk:179,64 private' failed with 'null'
07-31 04:06:15.909 30095 30095 E Sm : at android.os.Parcel.readException(Parcel.java:1628)
07-31 04:06:15.909 30095 30095 E Sm : at android.os.Parcel.readException(Parcel.java:1573)
07-31 04:06:15.909 30095 30095 E Sm : at android.os.storage.IMountService$Stub$Proxy.partitionPrivate(IMountService.java:1067)
07-31 04:06:15.909 30095 30095 E Sm : at com.android.commands.sm.Sm.runPartition(Sm.java:145)
07-31 04:06:15.909 30095 30095 E Sm : at com.android.commands.sm.Sm.run(Sm.java:77)
07-31 04:06:15.909 30095 30095 E Sm : at com.android.commands.sm.Sm.main(Sm.java:40)
07-31 04:06:15.909 30095 30095 E Sm : at com.android.internal.os.RuntimeInit.nativeFinishInit(Native Method)
07-31 04:06:15.909 30095 30095 E Sm : at com.android.internal.os.RuntimeInit.main(RuntimeInit.java:251)
07-31 04:06:15.912 30095 30095 I art : System.exit called, status: 1
07-31 04:06:15.912 30095 30095 I AndroidRuntime: VM exiting with result code 1.