For some caches you put the description twice into the GPX. I suspect this happens only for caches that require a password, since the description of such caches seems to be modified on the fly during GPX generation. Example caches: OU0ACB or OU0ACA. Just download their GPX and compare the long_description field against the description of the same cache in the website output.
Initially reported as bug in cgeo, but that issue occurs also without using cgeo: https://github.com/cgeo/cgeo/issues/6808.