WLAN - Maximum number of allowed devices per voucher limit has exceeded -> only with "Devices per voucher: 1"

Hello,

Sophos XG210 

SFOS 17.5.15 MR-15

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Hotspot Settings:

Hotspot type: Voucher
Voucher definitions:
  • 1 Day
  • 7 Days,1 GB
  • Mitarbeiter Voucher 180 Tage
Devices per voucher: 1
Administrative users: <Users from Active-Directory>
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Voucher were created in User-Portal for 1 and 180 days.
If you try to log in with an unused voucher (no matter which voucher), the following error message appears: "Maximum number of allowed devices per voucher limit has exceeded".
If we change "Devices per voucher" from 1 to 2 the enddevice can login with the voucher + another device (works as aspected).

We have two identical Sophos setups with identical settings at different locations. The voucher problem only occurs at one location.
Problem is: "Devices per voucher: 1" doesn't work. Devices per voucher: 2,3,4 or unlimited works as aspected
Tested multiple times.
Best regards