I just reached the end of a hardcore void crusade and entered the reward room. I wanted to make space in my inventory before opening the reward chests. 

• I opened the inventory screen and sorted by rarity.
• I started deleting blue items by clicking on them and pressing the delete key.
• Many items deleted succesfully.
• I tried to delete one pistol and it wouldn't delete, it remained in inventory.
• I tried to delete it again, and it continued to remain in inventory.
• I clicked to sort by type.
• It did not sort and inventory UI become unresponsive. I could not click on any buttons or items, but the animation continued to play in the background. Moving the mouse continued to move the background, but no elements of the UI were clickable.

I had to forcibly quit the game and relog in.

When I logged in the void crusade screen told me that the crusade was finished, but I didn't receive the seasonal completion for finishing and mastering a hardcore void crusade. My inventory also had nothing I had picked up during the final mission.

So I lost 1h 45 minutes of my time, the 7 shards used to create the crusade, all the items looted in the supreme mission up until the end, all the reward chests at the end of the supreme mission, and despite the crusade saying it was completed, I got no completion for seasonal objectives.