My Lore Triumph section is constantly flashing for unclaimed triumphs, under The Darkness. Using braytech.org, it appears that I've unlocked 4 triumphs under The Chronicon, but the tab itself still just shows ???????, so I can't claim them.
There are also three recent Reddit threads related to this - https://www.reddit.com/r/DestinyTheGame/comments/dk6v4n/the_darkness_lore_triumph_never_stops_flashing/ https://www.reddit.com/r/DestinyTheGame/comments/dkatkk/how_to_unlock_the_chronicon_lore_tab/ and https://www.reddit.com/r/DestinyTheGame/comments/dkqke0/bug_in_the_darkness_lore_book_section/ - but I can't find any further back. Given in the third link the poster says he's been experiencing this issue for two weeks as of one week ago, I'm guessing this was introduced in 2.6.0.1