Title. Duration info is present for the player. I assume LibClassicDurations is used, and other addons like WeakAuras and SUF can use it so that does not seem to be the problem. Works fine for debuffs, although I believe the API is different.

Did you enable durations in: General / General Tab / Auras Section / Enable Aura Durations option ?

What my frames show:

The left one is my own frame which displays duration correctly (currently have cooldown text hidden, using OmniCC), but does not work for other group members.

Can you confirm if the durations are displayed in another type of buff statuses ? You can create a single buff or the blizzard buffs status to do the test.

Try out version 1.1.7-alpha-classic, please report back if this fix works (i could not test the fix).
https://www.wowace.com/projects/grid2/files/3159618

Seems to work. Thanks for the help.