Sounds like they've corrected the bug that told you to send 12 months if you selected option 3, so there's nothing to worry about there.
As long as it's still telling you to submit only 6 months of payslips and bank statements, then Option 3 is correct, and you're good to go.
But if Option 3 does tell you to submit 12 months of payslips/bank statements, then change it to Option 1 instead.
Basically, just select whichever option you need to, so that it tells you to send 6 months and not 12 months.