How to find what is creating and killing so many buffers?

Question

A bunch of creating and killing buffers in my setup and I can't track down what is it. Here is my debug code:

(add-hook 'kill-buffer-hook
          (lambda() (message "Killed: %s / %s" major-mode (buffer-name))))

which results in something like this:

Killed: fundamental-mode /  *temp* [170 times]
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp*
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp*
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp*
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp*
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp*
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp* [234 times]
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp*
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp*
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp*
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp*
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp*
Killed: fundamental-mode /  *string-output*
Killed: fundamental-mode /  *temp* [220 times]

Sometimes it peaks a dozen a second. I swapped my .emacs.d with a Doom setup (my current is a Spacemacs heavily tuned) and those killings still happen, but seldom. Especially when idle, nothing is observed, while with my setup it's this very frequent and comes in batches. It's causing lots of slow downs, cursor movements are the main culprit, generating more than a bunch per move.