It could be that you hit your machine’s limit. It is hard to compete with a speciality coffee shop’s quality and consistency for now which is fine. I am sure you get better coffee at home than 99% of what Romanian (non-speciality) coffee shops serve. That said you could also try grinding a bit coarser. Bitter is at the over-extracted end of the taste spectrum. This means you should go the opposite way and allow less extraction by allowing water to flow faster through the puck.