Thanks for the reply, at least I know it is not just me.

I’m fairly new to lemmy so excuse me if I am telling you what you already know, but I have found out that at times when you can’t get onto feddit.ch due to the ‘server error’ fault, it is still possible to view and post to it from another instance. Create an account on another instance, then subscribe to whatever feddit.ch community you are following and usually it works. For example 2 hours ago when I posted the reply below I couldn’t login here at all whereas now I can (though I don’t know how long for). Maybe this suggests there is some configuration fault with the feddit.ch server that is randomly denying access from the wider internet whilst still allowing it from other lemmy servers, who knows?