Calibre error on 'Compress images'

I'm getting the following error on ePubs (also after reinstalling Calibre). I only select to 'Enable lossy compression of JPEG images':

Calibre, version 9.11.0
ERROR: Unexpected error: Failed to compress images, click "Show details" for more information

Traceback (most recent call last):
File "calibre\gui2\tweak_book\polish.py", line 348, in run_compress
File "calibre\ebooks\oeb\polish\images.py", line 172, in compress_images
File "calibre\ebooks\oeb\polish\images.py", line 151, in convert_png_to_format
IndexError: Replacement index 5 out of range for positional args tuple

Any ideas? Cheers!