Description: After re-joining the game (sometimes it can happen just while you play in your world) Calamity summons can despawn after 30-40 seconds of life, even if they're attacking an enemy.
How to cause it: by either just playing for a certain time, and using specifically Calamity's summon weapons or re-joining the world, it is inconsistent and can either happen or not.
Multiplayer: Did not test in multiplayer, so probably it's just in singleplayer.
I'm using Windows 10.
Yes, my PC has a dedicated GPU, I have 16 GB of RAM.
Note: Tried to disable the Boss checklist mod, it did nit fix the problem, the problem seems in calamity itself.