I am experiencing the same issue, but in my case I did not reinstall the OS. I run g2ax from a dedicated VM that is returned to its original snapshot after every use, unless I apparently am required to update the g2ax version and I create a new snapshot before doing any online stuff. The last time this was done was on July 3 and was related to an attempt to fix the saved credentials on the 1610 build.
As I found out yesterday, with a customer waiting, which annoyes the hell out of me, I am no longer able to log in with that very same build and it seems to me this must be related to the updated login service v1.23.0 from October 10. An interesting fact here is that the logo in the top of the login screen is missing and this seems to indicate some bad html/css/js coding in that page or at least ask for internet explorer features that were not in the previous version. The only version I can still login with is the 1544 build but this instantly upgrades me to the 1673 build that asks me to enter my credentials again on the crippled login page.