Alright - after 3 server crashes in 3 consecutive days, I was able to get a replacement server from my provider - thank you 
I set it up quickly - which I can do quite easily now due to the fact that I had to do it so often. There is always a bright side in things.. :)
Now: my witness got activated again last night and has produced so far 12 blocks - without miss.
As soon as my backup server is ready, I will set it up as well and then I can hopefully and finally sleep a little better.
Nevertheless, the last few days have taught me a lot and as 
missed blocks are like battle scars on a body of a proud warrior ( epic music plays in the background ), there's nothing wrong to have them, well, as long as you are a warrior and have a well-shaped body
It's part of being a witness to miss some blocks - the important points are:
1.) how to handle it when it happens
2.) what to do, to prevent it.
And I think I'm on a good path for both points!