GS305E not switching to 802.1q Advanced mode

[uthankeva]

Hi,

I have three GS305E switches which all have problems switching the VLAN mode
I'd like them all to run on 802.1q Advanced but always get the same problem:
upon switching the mode I get the popup that all other vlan configuration will be lost
but after pressing 'ok' nothing happens. The selection is greyed out and so are the delete/add buttons.
If I reload the page the previous configuration is still active.

Any help?
Thanks

[schumaku]

Just for completeness - which firmware is installed on these switches? Current https://www.netgear.com/support/product/gs305e.aspx#download ?

Which web browser? Already tried an alternate (or probably more common) Web browser?