Problem:
Buffer-updates on_detach callback is invoked before buf_freeall(), which
deletes autocmds of the buffer (via apply_autocmds(EVENT_BUFWIPEOUT,
...)). Due to this, buffer-local autocmds executed in on_detach (e.g.,
LspDetach) are not actually invoked.
Solution:
Call buf_updates_unload() before buf_freeall().