The style //!< is for documentation put *after* the member
being documented.
http://www.doxygen.nl/manual/docblocks.html#memberdoc
You can see how that's messing up the documentation of private
members here for example:
https://bitcoindoxygen.art/ABC/class_c_tx_mem_pool_entry.html
(Note there are still several files using //!< but correctly.)