Welcome! This forum has a treasure trove of great info – Scouters helping Scouters! Just a heads up, though - all content, information, and opinions shared on this forum are those of the author, not the BSA.
I have the same problem and hard refresh or cache deleting has not helped. How I go around it is I just manually type calendar in the browser address. I for example take the link https://advancements.scouting.org/roster then I delete roster and type calendar instead and this works for me
Thanks, @jacobfetzer for your response; no, I do not have any other issues with SB+. But perhaps something changed ?! this morning I have access again – and I wish I could tell you why.