When I have one of my regular teachers, they seem to understand my English, but when I have a new teacher, they have trouble understanding my pronunciation. They keep asking me to repeat myself.
この場合、次のような言い方ができますよ。
ーWhen I have one of my regular teachers, they seem to understand my English, but when I have a new teacher, they have trouble understanding my pronunciation. They keep asking me to repeat myself.
「馴染みの先生の時は私の英語を理解してもらえるようだけど、新しい先生は私の発音が通じなくて何度も聞き返してくる」
to have trouble understanding my pronunciation で「私の発音を理解するのに苦しむ」＝「私の発音が通じない」
ご参考まで！
カナダ 
