I have the same experience as you. I have been working with many non-native English speakers from different countries, and Americans (and to some degree Brits) are usually the ones who can't follow what is said. This improves over time as they get used to different accents, but it seems it is easier for non-native speakers to understand foreign accents than native speakers in general.
I'm not saying I always understand 100% of what is said. When someone with an accent from a specific part of a country speaks super fast and is on a poor line with lots of street traffic in the background, it can be hard to follow. But usually I catch enough of it to be able to communicate.
Normally I have had very good experiences as well. My colleagues almost always speak very good English and even those who don't are understandable. Everyone is happy to conduct meetings (with many nationalities, as I work in a scientific field) in English.
Only once have I encountered a problem. A colleague berated me in front of others for speaking "difficult English" and accused me of doing this on purpose to cause trouble for them, instead of speaking proper international English like everyone else did. But, I am a native English speaker with an RP accent and we were all in England at the time, working for a British organisation. I was simply speaking normally and otherwise had no issue with this colleague, whose English was very good. I don't recall their having been any misunderstandings between us before.
I'm not saying I always understand 100% of what is said. When someone with an accent from a specific part of a country speaks super fast and is on a poor line with lots of street traffic in the background, it can be hard to follow. But usually I catch enough of it to be able to communicate.