the doc of Postgres Ltree said that
A label is a sequence of alphanumeric characters and underscores (for example, in C locale the characters A-Za-z0-9_ are allowed). Labels must be less than 256 bytes long.
However, it does not said that if we set the locale to 'en_US.UTF-8', what is the valid character can be used in Postgres Ltree. So, can dash(hyphen) be used in the label of Ltree?
Sorry for not updating the answer.
Yes, i have finally figured out that it is one of our DBA that changed the source of ltree and recompile it with supporting the dash(-) char. We have a single table with more than 6B records.