Engraving inconsistencies

I have a crality Falcon pro 10w and used lightburn to engrave a few flasks. I used the same image and the exact same settings. However the first one came out great and the following ones seem to have banding issues.

I have no idea what could have caused it. Any recommendation/ideas?

Either the focus was slightly off (did you readjust it?) or the material had different properties, maybe it wasn’t flat.

I just attached two images for reference. It was the same focus and exact same flasks.

I only turned on and off my laser in between works.

I ran a few test afterwards and it seemed to engrave standard shapes without any problems. I’m very confused on what may have happened and how to prevent it