Thanks for the responses. I finally figured it out.
TL;DR: calendar programs apparently don’t like the windows ^M control character.
We had tried delete-&-resubscribe numerous times. This affected iOS & Android users and basically everyone in the troop. Even subscribing directly to a google calendar (in a new account that never subscribed to the troop calendar) via google’s web app calendar yielded the same results
It came down to an entry where someone copy-pasted the description from a word doc. The description had a bunch of windows carriage-returns (^M), some single, some double. While manually scrolling through the ICS file, I saw that every event listed after the entry with ^Ms would not appear when imported or subscribed. I’m not sure if it was the single ^M or double ^M^M that did it.
After I deleted the carriage returns from the ICS file, it imported fine into my calendar program. Editing the entry in ScoutBook+ to remove the offending ^Ms allowed the recently added events to finally appear on subscribed calendars.
One interesting side note, the open-source Thunderbird email/calendar program was the only application that ate the ^Ms and still showed the full calendar.
We’re going to implement a new TTP for our troop’s calendar maintainer: no copy-paste from Word docs… 
