Impossible to change LAN Network Mask to type B network

[rgolubev]

Hi there,

Device Model/Firmware: TG798vac V2 VANT-6 (iiNet)
GUI Version: [9.6.65-89342d7b] (https://github.com/Ansuel/tch-nginx-gui/releases/tag/9.6.65)

Please go to Cards >> GUI Settings >> Debug Report and press the Generate button.
Attach the debug file here:
DebugHelper2023-12-31-1424.tar.gz

Description of problem, HOW TO REPRODUCE, Media/Photos:
Before I updated to the new GUI, the original GUI allowed me to change LAN network mask to 255.255.0.0 while with the new one I get this error:

Cheers,
Roman