I just noticed the same problem here with NC 20.0.5. My team don’t see the shared calendar anymore. But it seems I cannot create shares again, I don’t know why. No errors in NC and PHP logs.
I had the same issue after updating from NC 20.0.4 to 20.0.5 (with Calendar 2.1.3 now, not sure about before the update). Two calendars that I shared with the same group were still visible in the account that created them, but for none of the users in the group.
In my case I identified the issue as the group name containing a space - once I had assigned all users in that group to an additional group that did not contain a space in its name, the sharing worked again.
It seems as if a similar issue also existed in the past with group names containing a slash (Sharing Calendar Fails: Shared Calendar Does not Appear - #5 by mrw), so maybe this is also the case with other special characters in group / user names now.