Gimp make jpg to Webp 100% quality half size while IM6 make double size. why?

[estatistics]

Yes you are right! Gimp lossless creates bigger files than the size of the original JPG. However, the IM6 lossless still produce somewhat larger sizes in 100%.

stat *
File: DSC_1528_gimp100_nolossless.webp
Size: 1,986,982

File: DSC_1528_gimp100_lossless.webp
Size: 5,986,002

File: DSC_1528_IM100.webp
Size: 6,064,204

original jpg
3,665,275

i didnt checked about exif iptc tables and other info. maybe the slight difference is somewhere there.