Issue with same inputs. One worked, the other not

[Nay]

Hello,

I've been using hashcat on a md5 Cisco type and I ran the following issue.


First time I used :
hashcat -m 500 -a 3 -1 ?l?d?u '*****' ?1?1?1?1
And it ran exhausted. Then as  I wanted to compare speed, I've tried with the optimized version before trying longer masks :

hashcat -O -m 500 -a 3 -1 ?l?d?u '*****' ?1?1?1?1

The second was indeed way more fast, but what happened is that it cracked it on that second attempt. As the -O only optimizes the work, how could the first one not cracked it while the second did ? I really didn't get it.

Thank you for your opinion on this matter.

Note : As this was part of a challenge, I've changed some information with ****

First :

Session..........: hashcat                                
Status...........: Exhausted
Hash.Type........: md5crypt, MD5 (Unix), Cisco-IOS $1$ (MD5)
Hash.Target......: *******
Time.Started.....: Sat Jul 21 23:51:31 2018 (4 mins, 37 secs)
Time.Estimated...: Sat Jul 21 23:56:08 2018 (0 secs)
Guess.Mask.......: ?1?1?1?1_*** [11]
Guess.Charset....: -1 ?l?d?u, -2 Undefined, -3 Undefined, -4 Undefined
Guess.Queue......: 1/1 (100.00%)
Speed.Dev.#2.....:    37642 H/s (2.59ms)
Speed.Dev.#3.....:    11951 H/s (2.05ms)
Speed.Dev.#*.....:    49593 H/s
Recovered........: 0/1 (0.00%) Digests, 0/1 (0.00%) Salts
Progress.........: 14776336/14776336 (100.00%)
Rejected.........: 0/14776336 (0.00%)
Restore.Point....: 236456/238328 (99.21%)
Candidates.#2....: XB7Q_*** -> XQzF_***
Candidates.#3....: XNBw_*** -> XC9Z_***

Second :

****:*****               
                                                          
Session..........: hashcat
Status...........: Cracked
Hash.Type........: md5crypt, MD5 (Unix), Cisco-IOS $1$ (MD5)
Hash.Target......: ******
Time.Started.....: Sat Jul 21 23:57:25 2018 (33 secs)
Time.Estimated...: Sat Jul 21 23:57:58 2018 (0 secs)
Guess.Mask.......: ?1?1?1?1_*** [11]
Guess.Charset....: -1 ?l?d?u, -2 Undefined, -3 Undefined, -4 Undefined
Guess.Queue......: 1/1 (100.00%)
Speed.Dev.#2.....:    85297 H/s (11.17ms)
Speed.Dev.#3.....:    85752 H/s (5.38ms)
Speed.Dev.#*.....:   171.0 kH/s
Recovered........: 1/1 (100.00%) Digests, 1/1 (100.00%) Salts
Progress.........: 5603328/14776336 (37.92%)
Rejected.........: 0/5603328 (0.00%)
Restore.Point....: 73728/238328 (30.94%)
Candidates.#2....: 66rj_*** -> 6w5e_***
Candidates.#3....: mOsj_*** -> mIt4_***