I definitely have had this issue. I'm a native English speaker and taught in Europe for a few years, where a subset of students had trouble understanding me, mo

I definitely have had this issue. I'm a native English speaker and taught in Europe for a few years, where a subset of students had trouble understanding me, mostly because I would just drop too many consonants and run words together. E.g. if speaking quickly, I tend to pronounce "because" as one syllable, something like "biz". I've moved towards much more consciously enunciating words in mixed-nationality settings. Americans now sometimes think I sound foreign though!