I believed I had this experience too, 2 days ago. Near the end of one fruitful seasonal mission, I summoned a season skull from a temple, but nothing dropped after it met its demise.

Maybe characters with high "loot quantity" could run into this issue more often.

I also remembered that during that mission, I changed auto-pick filter from picking all to only picking items above (including) artificer quality. Don't know if this is related, just mention it here.

Also, an update: it seems that with the weekly buff increasing item dropping rate, he also experiences this issue much sooner.

So this issue might be related to the number of items that have been dropped during one mission:  after certain amounts have been reached, no more items and credits would drop from these enemies.

Hi Marco:

Here's the share link of the video:

https://drive.google.com/file/d/1OwojjFNGbPsEQbPWJ5ObN9LIbUC3U7sX/view?usp=sharing

From 03:10 of this video and until it ends at 04:45, items seem to stop dropping from regular enemies (still some dropping from destroyable objects). 

It looks quite obvious if you compare this period with 01:00-01:15, when the drop rate behaves normal.

Hope it helps. If you need further information or if you cannot gain access to the video please let us know :)

Maybe it's convenient just look at the Seasonal one.