I’m just a unit ASM, but yes, there appears to be at least in part, a bug. See this post for the thread I linked to:
https://discussions.scouting.org/t/who-has-permission-to-assign-merit-badge-counselors-now/510295/22
Note that the bug is not apparently that UAC don’t have automatic permissions to do this (as Ed noted). The bug appears to be that the permissions delegation system for this is (or at least was 9 days ago) not working quite right.
In the interest of full disclosure, I tend to agree with the Guide to Advancement position – not that national asked me or would likely care about my opinion – that the SM or their designee should be having that conversation with the scout. If the designee in your unit is the UAC, then the SM or one of the unit Key 3 can assign the relevant permissions (once they’re working again). The UAC is not that designee in my unit, for example. So, it would be potentially problematic for us if some future UAC was connecting scouts to MBCs when the SM hadn’t discussed starting the MB with the scout. The beauty of the new permissions structure is the finer granularity of the permissions. The headache is the need to set them, particularly as we’re all transitioning over from the prior system.