Model comes with fringes

Dear community,

We are working with an elongated particle, of about 250x20x20 A, with C2 symmetry.

In the first datasets we processed, all models (from 2D class and further 3D models/refinement) seem to have periodic horizontal fringes, as attached. This is true for cryosparc, but also for relion. We believed at first that it might be some interference from data collection, so we collected a second dataset that turns out to have the same issue.

I wonder now if this might be anything related to the way softwares do the alignment, or any other thing we are missing.

Any help will be appreciated