Full debug session can be read in https://matrix.to/#/!ikPtGZaGWtyblizzlR:matrix.xwiki.com/$1706796616756ozyrz:matrix.xwiki.com?via=matrix.org&via=matrix.xwiki.com&via=helsinki-systems.de

TL;DR: we don't know where the ClassCastException comes from, even after reviewing the converters from XS. It's not clear why there's no stacktrace and no specific message for that ClassCastException, it's happening as if something was throwing an empty ClassCastException somewhere. We need a proper reproduction steps or a debug session when it's happening to actually understand the bug.