I've noticed same issue;
I'm on a Mac, Corona beta8
Full-speed non-debug version
Build timestamp: Sep 15 2021 22:27:46
Version: 8 (DailyBuild Sep 15 2021)
Cinema version: R25.010 Cinema 4D.
just like Tuami says, the issue seems to be correlated to sky object visibility attributes; visible in refraction, and reflections (more drastically). Physical or HDR sky don't make difference. Also roughness <0 value in glass refraction channel play a role; if visible in refraction is unchecked in sky object, no issues if glass refraction is perfectly smooth.
Hope this help,
all the best,
Rutg3r