I don't quite grasp you saying you have to "sign-in" to Bing to get to MS Rewards. But, I understand you to say neither will work for you in Dev. So, I thought I would give it a try. Bing (bing.com) opens (loads) signed-in to me & the same goes for MS Rewards (https://account.microsoft.com/rewards/?refd=www.microsoft.com). Either I cannot repro the issue OR I'm not correctly understanding what you describe.
Have you tried uninstalling & re-installing Dev using a fresh download of it?