Mausoleum Delirium map - no drop after killing everything

hello,
I got a Mausoleum Delirium map (T4), after killing and steeping on everything the map reward dosent show up :

https://drive.google.com/file/d/1nhDm85HG1ZJwkb13ESA5FJ8vaCaAUUKX/view?usp=sharing

Monster remaining : 0 (and all Nemesis killed)

ref : 2,638,381,502

If the map contains layers of delirium, you receive the drops immediately as you fill the rewards, rather than when the delirium ends (since, of course, it never ends).

when you said immediately, does this mean at each milestone when killing mobs ?
if that's the case, i didn't get any reward when reaching a new milestone
(also, is it normal that the gauge isn't full when i actually killed/stepped on everything ?)

You are correct on both accounts.

And its likely that items were dropped at the new reward tier and you associated it with regular monster drops since you were not expecting them or your loot filter potentially hid the drops.