Hi [member=47]eti[/member],
It seems I have been able to replicate the issue, and have found the way to Vote when this issue appears.
[member=5]ALVINI[/member] (Viktors) just had the same issue > manually selecting all voting masternodes resolved this issue.
1) click on 'vote'
2) selecting masternodes to vote:
2.1) if you haven't voted before >> click on 'select voting masternodes'
2.1) if you have voted before >> click on 'change votes'
3) now you need to manually select the masternodes (please do not us 'select all' option)
after this, click on the button 'select votes', of course
4) the last window: click on 'Yes' (or 'No', if you are against a proposal), and click on the button 'vote'
That is it.
Did this help? .. We will look into this strange issue, though, no promisses on quick fix.
Best wishes!!
Helmuts