HashCat failes to bruteforce crack a known hash.

Q: Why is has hashcat failing to crack a known WPA2 hash?

Background: WPA2 access point (mine), known 8 character random alpha numeric password with mixed case i.e. e4rrT4er, has survived (= FAILED Hashcat!) a brute force HashCat attack.

** WHY?? ** or How, more accurately....

Given that I've specified HashCat to try every possible combination of 8 characters passwords in its bruteforce attack, the hash should have been cracked...

v1.36

Command line used:
./cudaHashcat64.bin -m 2500 -a3 ./mytestap.hccap ?d?d?d?d?d?d?d?d -o password.txt

Output after 1.5H:
INFO: approaching final keyspace, workload adjusted


Session.Name...: cudaHashcat
Status.........: Exhausted
Input.Mode.....: Mask (?d?d?d?d?d?d?d?d) [8]
Hash.Target....: mytestap.hccap
Hash.Type......: WPA/WPA2
Time.Started...: Thu Jun 11 13:45:14 2015 (1 hour, 30 mins)
Time.Estimated.: 0 secs
Speed.GPU.#1...: 17247 H/s
Recovered......: 0/1 (0.00%) Digests, 0/1 (0.00%) Salts
Progress.......: 100000000/100000000 (100.00%)
Rejected.......: 0/100000000 (0.00%)
HWMon.GPU.#1...: -1% Util, 74c Temp, 47% Fan

Started: Thu Jun 11 13:45:14 2015
Stopped: Thu Jun 11 15:15:38 2015

System Info:
Device #1: GeForce GTX 550 Ti, 1023MB, 1800Mhz, 4MCU

Hashes: 1 hashes; 1 unique digests, 1 unique salts
Bitmaps: 16 bits, 65536 entries, 0x0000ffff mask, 262144 bytes, 5/13 rotates
Applicable Optimizers:
* Zero-Byte
* Single-Hash
* Single-Salt
* Brute-Force
Watchdog: Temperature abort trigger set to 90c
Watchdog: Temperature retain trigger set to 80c
Device #1: Kernel ./kernels/4318/m02500.sm_21.64.ptx
Device #1: Kernel ./kernels/4318/markov_le_v1.64.ptx
Device #1: Kernel ./kernels/4318/amp_a3_v1.64.ptx


What going on?