Did you fix that bug with the portal block?
There are no known crash bugs when placing / using the portal block. However, if the world files and Mining Portal NBT data is corrupted due to any reason, there is no easy method to forcibly reopen a portal link (with mining portal blocks). This is something I have been thinking about implementing, but work is not ongoing.
It should no longer be a problem to use link books / other means of moving between dimensions however, since clients are now informed about all existing mining dimensions when they join a server.