Huh, nice (?) discovery. I confirm the same problem on my rooted (and microG'd) device. SIM comes up with with "normal boot", not present with "rooted Android" boot. I haven't tested SIMs in my device recently, so I hadn't noticed this development.
Edit: Oh, I notice now that "normal boot" on my device is still coming up rooted, so I expect that's still booting the Magisk'd boot.img provided by Ninji
here, so the problem would appear to have something to do with the rooted image from Cosmo, not with the mere fact that the device is rooted (and microG'd).
Would be nice to hear input from people who have rooted with Cosmo's root.img and *not* installed microG.