GIF thumbnails are not generated

[thecoffeebin]

On Seafile 12.0.4 CE with docker.

Managed to see JPG and PNG thumbnails generated on the web UI, but not GIF.

seahub.log (if it helps)

2024-12-10 01:28:10,044 [WARNING] seahub.thumbnail.utils:155 generate_thumbnail cannot write mode P as JPEG
2024-12-10 01:28:10,050 [WARNING] django.request:241 log_response Bad Request: /thumbnail/977356c9-2e19-4d99-a3c6-e09c3aae38d2/create/
2024-12-10 01:28:10,375 [WARNING] seahub.thumbnail.utils:155 generate_thumbnail cannot write mode P as JPEG
2024-12-10 01:28:10,381 [WARNING] django.request:241 log_response Bad Request: /thumbnail/977356c9-2e19-4d99-a3c6-e09c3aae38d2/create/
2024-12-10 01:28:10,848 [WARNING] seahub.thumbnail.utils:155 generate_thumbnail cannot write mode P as JPEG
2024-12-10 01:28:10,854 [WARNING] django.request:241 log_response Bad Request: /thumbnail/977356c9-2e19-4d99-a3c6-e09c3aae38d2/create/
2024-12-10 01:28:11,171 [WARNING] seahub.thumbnail.utils:155 generate_thumbnail cannot write mode P as JPEG
2024-12-10 01:28:11,173 [WARNING] django.request:241 log_response Bad Request: /thumbnail/977356c9-2e19-4d99-a3c6-e09c3aae38d2/create/
2024-12-10 01:28:11,489 [WARNING] seahub.thumbnail.utils:155 generate_thumbnail cannot write mode P as JPEG
2024-12-10 01:28:11,494 [WARNING] django.request:241 log_response Bad Request: /thumbnail/977356c9-2e19-4d99-a3c6-e09c3aae38d2/create/
2024-12-10 01:28:11,819 [WARNING] seahub.thumbnail.utils:155 generate_thumbnail cannot write mode P as JPEG
2024-12-10 01:28:11,825 [WARNING] django.request:241 log_response Bad Request: /thumbnail/977356c9-2e19-4d99-a3c6-e09c3aae38d2/create/
2024-12-10 01:28:12,166 [WARNING] seahub.thumbnail.utils:155 generate_thumbnail cannot identify image file <_io.BytesIO object at 0x7f9ddec25ad0>
2024-12-10 01:28:12,167 [WARNING] django.request:241 log_response Bad Request: /thumbnail/977356c9-2e19-4d99-a3c6-e09c3aae38d2/create/
2024-12-10 01:28:12,481 [WARNING] seahub.thumbnail.utils:155 generate_thumbnail cannot write mode P as JPEG
2024-12-10 01:28:12,486 [WARNING] django.request:241 log_response Bad Request: /thumbnail/977356c9-2e19-4d99-a3c6-e09c3aae38d2/create/
2024-12-10 01:28:12,820 [WARNING] seahub.thumbnail.utils:155 generate_thumbnail cannot write mode P as JPEG
2024-12-10 01:28:12,825 [WARNING] django.request:241 log_response Bad Request: /thumbnail/977356c9-2e19-4d99-a3c6-e09c3aae38d2/create/
2024-12-10 01:28:13,180 [WARNING] seahub.thumbnail.utils:155 generate_thumbnail cannot write mode P as JPEG
2024-12-10 01:28:13,182 [WARNING] django.request:241 log_response Bad Request: /thumbnail/977356c9-2e19-4d99-a3c6-e09c3aae38d2/create/

This is even the case for the official Seafile Demo (https://demo.seafile.com/) where GIF thumbnail is not generated. I'm surprised no one asked before.