For a while now the server has been continually hit with login attempts. It got to such a point this morning that the logs, that record the login attempts, had used up all of our disk space on the server.
This also had the effect of locking me out of the server and it has taken most of today to get the server to reboot so l could access it.
Once rebooted l found that the forum had corrupt messages_table which also had to be repaired.
I cannot say if the the login attempts has contributed to the slowness some have experienced, but it may have done.
I will now arrange to move the forum to another server host in the next few days (one that answers their ticket system l hope!).