Software rendering bad quality

How does it happen that the result between software render and GPU Cuda render has different results in quality and file size?

I had to use software renderer for some time because my AE (and the Media Encoder) crashed multiple times after the 2022 update while rendering.

File Size (same sequence):

Software: 9mb

GPU Cuda: 7mb

Quality:

Software:

GPU Cuda:

It's 100% the same file and settings, I rendered the first, reset the queue, changed the name and swapped the renderer.

The text is created in 4k in AE inserted as AE sequence into Full HD Premiere squence and exported as Full HD in Media Encoder.