Since https://issues.apache.org/jira/browse/LUCENE-8548 the Korean tokenizer groups characters of unknown words if they belong to the same script or an inherited one. This is ok for inputs like Мoscow (with a Cyrillic М and the rest in Latin) but this rule doesn't work well on digits since they are considered common with other scripts. For instance the input "44사이즈" is kept as is even though "사이즈" is part of the dictionary. We should restore the original behavior and splits any unknown words if a digit is followed by another type.
This issue was first discovered in https://github.com/elastic/elasticsearch/issues/46365