Calling toString() in the middle of decoding a repeating group breaks the decoding of that group. For example, subsequent entries are skipped:

for (MyGroupDecoder member : decoder.myGroup()) {
    logger.debug(decoder);
    handle(member.myValue());
}

Only the first member of the repeating group will be handled.

The fix should be pretty simple: generate code into the appendTo method to save and restore index and offset when handling each group, similar to how it already saves and restores limit.