SOUNDS MIXED UP FOR THE JAPANESE COURSE
anyone else going through this issue?
Ro's sound is probably correct, as the best way I can describe the Japanese "r" sound would be a combination of English's "r", "d", and "l" sounds. So it probably just sounds like a "d" sound to you, which is understandable.
As for the "s instead of su" sound, that's pretty common among natives, with many words. However, Duolingo doesn't explain this (as far as I know), so I don't blame you for thinking it's wrong.
“S” instead of “su” is relatively normal, actually. The verb for “to like”, which in Hiragana only is すき, it pronounced “ski” instead of “suki”. When I took a Japanese class I was told “don’t pronounce it like ‘suki’ unless you want to sound like an old woman,” but if you listen closely to any Japanese audio, like in anime, you’ll notice that they tend to have a quiet-but-not-quite-there “oo” sound in some words where “u” is between consonant sounds (including the word すき).
As for the sound “ro”, the “r” sound in Japanese is actually closer to an “l” sound, and because it’s alveolar (meaning behind the teeth, unlike the English throaty “r”) and a tap, it can sometimes sound more like a “d”, and this happens in other languages too, even when the “r” sound is distinct from the “l” sound (i.e, Spanish). Think of the Japanese “r” as between the English “r” and “l” since there’s no L sound in native Japanese and it’s replaced with “r” in loanwords.
The example you give with すき is referred to linguistically as vowel devoicing. The う in す is given reduced emphasis and the syllable ends up being pronounced over a slightly shorter period. The う is still pronounced though, and most Japanese speakers should be able to notice if it's not there. Vowel devoicing is less common or absent in more careful or less casual speech.