The server is now running again.
The problem appears to have been related to me setting the pakset settings to override the saved game settings. For reasons which I have yet to be able to trace, setting this seems to have caused the maximum number of alternative destinations for passengers (but, oddly, not the minimum number) to be set to an unreasonably high level. This is what caused the performance issues witnessed by those attempting to play yesterday.
These incorrect data seem to have been generated on the server. Unfortunately, I have not been able to reproduce this, so I cannot find the ultimate cause. Fortunately, unsetting the option for the pakset simuconf.tab to override the saved game settings reversed this problem, and, as the correct number of alternative destinations is calculated monthly, the incorrect number has now been replaced with the correct number, and performance has returned to normal.
My apologies for the difficulties: people should be able to connect now as previously.