Wpa speed dropping

Hello there,

Can some one tell me why my wpa speed slow's down about 30sec after starting. Just bought my new pc last week.
Device #1: GeForce GTX 1080, 2048/8192 MB allocatable, 20MCU

Session..........: 2018-08-01
Status...........: Running
Hash.Type........: WPA/WPA2
Hash.Target......: C:\Program Files\HashcatGUI_1.00r3\hashcat-4.1.0\vm1.hccapx
Time.Started.....: Wed Aug 01 18:36:33 2018 (2 secs)
Time.Estimated...: Sat Aug 04 17:10:11 2018 (2 days, 22 hours)
Guess.Mask.......: ?1?1?1?1?1?1?1?1 [8]
Guess.Charset....: -1 abcdefghjklmnpqrstuvwxyz, -2 Undefined, -3 Undefined, -4 Undefined
Guess.Queue......: 1/1 (100.00%)
Speed.Dev.#1.....:   433.3 kH/s (91.33ms) @ Accel:64 Loops:128 Thr:1024 Vec:1

Session..........: 2018-08-01
Status...........: Running
Hash.Type........: WPA/WPA2
Hash.Target......: C:\Program Files\HashcatGUI_1.00r3\hashcat-4.1.0\vm1.hccapx
Time.Started.....: Wed Aug 01 18:36:33 2018 (26 secs)
Time.Estimated...: Mon Aug 06 22:52:02 2018 (5 days, 4 hours)
Guess.Mask.......: ?1?1?1?1?1?1?1?1 [8]
Guess.Charset....: -1 abcdefghjklmnpqrstuvwxyz, -2 Undefined, -3 Undefined, -4 Undefined
Guess.Queue......: 1/1 (100.00%)
Speed.Dev.#1.....:   246.1 kH/s (91.72ms) @ Accel:64 Loops:128 Thr:1024 Vec:1

Am I missing something

Cheers Kev