I've chosen the name a bit at random, but for reason I don't understand I have trouble hearing the initial r-sound on several of my male Japanese students' names. Two examples chosen someone at random: 隆介 and 綾

They say りゅうせすけ and りょう but I hear ゆうすけ and よう

I'm a native English speaker of American English but also had experience hearing German as a child in Germany. Is there some linguistic issue going on here or do I just need to get my ears checked?

I saw this question: Utterance initial [ɾ] which explains some of the mouth position for the sound. But, it doesn't answer what I'm asking.