Those usually indicate a first layer printing too low - go through a regular maintenance session ( https://help.prusa3d.com/article/regular-printer-maintenance-core-one_829710 ) then run the setup calibrations again - come back if the problem persists.
Cheerio,
RE: Why am I getting these ridges
That looks like the Prusa Satin sheet? I had the exact same problem occur after I purchased and used a brand new sheet. Using an older Satin sheet under the same conditions gave me a perfect smooth layer except the sheet was a bit banged up (2 years old). Prusa send me a new sheet and the problem went away. I think in my case it was an issue with adhesion.
RE: Why am I getting these ridges
If this is a new spool of filament, they can vary batch to batch, one being thicker than the next (that +-0.05 spec), and filament that is wet can also cause issues since it tends to swell. Doesn't sound like much but a few percent can make a change in the layer one results. Try reducing flow to 95%, see if the issue stops. You can do that while watching the print, drop down until no ridges are seen. Then when the second or third layer starts, set things back to 100%.
Calipers or better micrometers can help resolve filament diameter problems, too.
RE: Why am I getting these ridges
Sorry for the extra post - web site is ignoring the EDIT button: but I've noticed on my new Core One there is a rather large print to print variation in layer one depth. Some will have minor ridging, some minor gaps: and the print sheet isn't removed between print... so its in the pressure sensor setting nozzle height that's the issue: just not as consistent as the old proximity detectors, I guess.
RE: Why am I getting these ridges
Thanks, after recalibrating the z axis, cleaning the plate well with 99% IPA, and switching to the smooth plate, I stopped having the issue and haven't seen it again since, even on other large flat prints.