We had this issue on a few sites recently after logo .jpg images were swapped to .webp format.
I initially suspected a conflict between the host’s (BionicWP) native caching solution and WP Rocket which was installed by someone else on the team.
My initial suggestion – based on Leo’s suggestion – was try to replace the .webp logo with a .jpg image. But they had contacted BionicWP in the meantime.
Here is what BionicWP had to say:
This is not a plugin conflict. We are now using a new and improved algorithm to filter unused CSS and to make pages even lighter and faster than before. The filtered CSS required some basic CSS to be defined for elements and this is why the logo was enormously large. A simple line of CSS code has fixed the issue.
This was their CSS fix:
.site-header .header-image {display:block;}
Not sure if this helps anyone, but GP devs may want to possibly include this CSS in a future release to avoid this issue on similar environments.
All the best,
Paul