descrypt-ztex: attacks without big mask cause timeouts and "task already completed" errors on underclocked boards

Using too small mask or attack without mask and setting frequency on for decrypt-ztex lower than default 190, I get rather frequent timeouts with 1 ztex board. Also I get "PROCESSING_DONE id=1: task already completed" errors. It does not seem to happen with big masks like '?w?a?a?a'.

$ echo AAnfJdS9QQ3FE > t.pw  # crypt.crypt('8Cx6UO2n', 'AA')

$ printf '.include <john.conf>\n[ZTEX:descrypt]\nFrequency = 180\n' > d.conf

$ john t.pw --incremental --mask='?w?d' --config=d.conf
ZTEX [...] bus:4 dev:4 Frequency:180 180 180 180 
[...]
SN [...]: Timeout.
Found 1 device(s) ZTEX 1.15y
SN: [...] productId: 10.15.0.0 "inouttraffic JtR 1.8.x" busnum:4 devnum:4 
SN [...]: Timeout.
Found 1 device(s) ZTEX 1.15y
SN: [...] productId: 10.15.0.0 "inouttraffic JtR 1.8.x" busnum:4 devnum:4 
SN [...]: Timeout.
Found 1 device(s) ZTEX 1.15y
SN: [...] productId: 10.15.0.0 "inouttraffic JtR 1.8.x" busnum:4 devnum:4 
SN [...]: Timeout.

Found 1 device(s) ZTEX 1.15y
SN: [...] productId: 10.15.0.0 "inouttraffic JtR 1.8.x" busnum:4 devnum:4 
0g 0:00:01:29 0,00% (ETA: 2022-07-05 15:38) 0g/s 6927Kp/s 6927Kc/s 6927KC/s ntsff21..1776j8
SN [...]: Timeout.

Found 1 device(s) ZTEX 1.15y
SN: [...] productId: 10.15.0.0 "inouttraffic JtR 1.8.x" busnum:4 devnum:4 
[...] #1 PROCESSING_DONE id=1: task already completed
[...] #1 PROCESSING_DONE: keys=65535, mask=10, processed=655370 (must be 655350)
SN [...]: bad input packet.

Found 1 device(s) ZTEX 1.15y
SN: [...] productId: 10.15.0.0 "inouttraffic JtR 1.8.x" busnum:4 devnum:4 
0g 0:00:01:59 0,00% (ETA: 2023-07-10 13:48) 0g/s 5274Kp/s 5274Kc/s 5274KC/s ntsff21..ayaamc7
Session aborted