/tmp full but... empty

In a Python program, I use np.memmaps, which make use of the /tmp directory to handle massive arrays.
I make sure to clear /tmpregularly by running rm -rf /tmp/* every time I use this code. However recently, my code stopped working and threw me a "Bus error (core dumped)".

Now, even using auto-completion in the terminal results in: bash: cannot create temp file for here-document: No space left on device.

typing df -h gives me, I think, the culprit:

tmpfs            32G   32G     0 100% /tmp

However, running sudo rm -rf /tmp/* only puts me back to

tmpfs            32G   30G  1,9G  94% /tmp

Any idea what is going on and how to fix it?

sudo lsof -n | grep /tmp |grep deleted