I may be the only person to ever reach a point where this could be a problem but I didn't get a warning when I reached capacity on hell pumpkins. I know I lost at least one pumpkin this way, possibly more.

Additionally, after I exchanged my pumpkins when I returned to the island I discovered that there was no pumpkin waiting for me to pick up now that I had room again.

Thank you for reporting!

We modified the loot items log entry, so now it tells if you don't have enough place to take the item looted from a monster.

Concerning the second part of report, it's not possible to pick up the lost loot from monsters. It works just the same way as looting Beast Temples.

Sorry for the inconvenience.