I won't go back all the way to 2009 when I bought my first pair of IEMS, but the most recent problems that I remember was Surise earphone enclosure opening because there was simply not enough glue. This is dangerous because you can rip the circuit board from the driver without it.Then TRN IEM had it's connector pushed inside the enclosure. Again, nothing that can't be fixed with glue. The rest were Sure IEM cables that people want fixed because they can't find replacement. Any cable with a microphone will have these issues, because these cables are so delicate and third party replacements often don't have the functions that people want like three button control or quality of the mic.
The hygene part I don't think I need to explain apart from things that use tuning filters at the tip, which of course will get dirty, you'll try to clean it and you'll lose one in the process.