Cannot delete queued actions in v20.3

Before upgrading to v20.3, we were able to delete any queued event by clicking the [X] that's shown next to it in the Pending Activity section of the General tab, as below:

But in v20.3, when you click the [X] you get the following error:

Session not in specified group, or you do not have permission to perform this operation on it.

I tried deleting the queued event from within different session groups. I also tried doing it as the Cloud Account Administrator rather than as the instance's administrator, but to no avail.

I was also able to replicate this on my on-premises server with v20.3.

So, basically, I can't delete queued actions anymore.

EDIT: This bug seems to occur in v20.4 too.