Little more here, I had this same issue. Carrying 65 Spectral Pages, wearing a masquerader's hood with Dominus Ghaul mask, already completed Gone but Not Forgotten (and unlocked all lore books), 4 spots free in inventory. Also holiday bounties were not progressing. Completed 4 HLS, received one Braytech auto-rifle at the completion of one directly to my inventory, no removal of spectral pages, no loot from completion chest, no activity completion weapon xp/deepsight progress. Troubleshooting: Changed mask ornament (tried multiple, including removing the ornament) - Did nothing Different Masquerade Hood - Did nothing Cleared my download cache in Steam and verified game integrity - Did nothing Completed a strike (which also obtained more pages) - Fixed
You may want to play this event on another character to see if that helps with your issue.