Announcements posted in Ultra Course View courses prior to December 12 2020 show that they have been viewed by all users on the course, whereas this was not the case before.
This issue seems to have arisen after one of the recent releases - possibly Learn SaaS release 3900.2.0, applied on the 3 December, which subsequently had various updates applied.
One of maintenance updates was applied on December 11 2020, which appears to coincide with the fact that from December 12 onwards we see information that suggests that anywhere between 50 - 90% of users have viewed the announcements posted from December 12 onwards, in large courses.
However, anything posted prior to December 12 shows 100% of users having viewed every announcement posted, which is not correct.

Observed Behavior:
All courses prior to X Date have 100% of views.
​Expected Behavior:
Having a 100% views is a very uncommon, specially since after X Date, rates seem back to normal.

Will Not Fix