I did further debugging...
It is indeed our 213.222.29.194 gateway that has the issue, it misses most
of the routes at least since yesterday (I notice because I have some mail
in the queue routed over IPIP that has stalled since yesterday).
But I do have another independently hosted IPIP host in the Netherlands
that receives all the normal routes. It is at IP 89.18.172.156
and is located in another datacenter.
So likely it is a routing issue on the internet...
Rob