This took me a while to figure out. So, I’m putting it up where it can be found via internet search.
Link to FB post re: these shareerrors: https://www.facebook.com/groups/TheLoopedGroup/2328447640705222/?comment_id=2328923923990927¬if_id=1565370121155952¬if_t=group_comment_follow
Link to Zulip discussion: https://loop.zulipchat.com/#narrow/stream/148543-Loop/topic/Dexcom.20Share
Photo of Zulip discussion (if you aren’t on Zuplip):
Date of this post: Aug 8, 2019
Solution: Rebuild Loop if you haven’t done so in the last 2 weeks.
Summary: BT is working fine. Transmitter Id fine. Firmware on my new transmitter (id 81XXXX) is funky. Need to rebuild with the newest version of Loop. This threw me for about a month since I first installed Loop. It is fixed now.