I still say the issue is with your PC. I suppose it COULD be your logon, but I doubt it. You might send a PM/email to IB's support people.

Cookie updating goes thru Windows "Defender" and Windows' Firewall, I know I have fought some ODD issues with both of those at work, when trying to get SIP sessions to behave properly in our console apps.

It would be interesting to see what IB's tech people say about it.