Unless Roon have moved their hosting (or added a POP in Europe) that’s a bit strange.
I see from your profile you are in Berlin and Roon is hosted (AFAIK) by Fastly in California. Based on distance alone you shouldn’t be getting response times less than 90mS
Maybe (though are we sure there is no CDN with servers elsewhere?), but I don’t think I would notice a lag of 0.09 seconds (or two, three times that) when searching. Maybe I’m just not sensitive to that / am not expecting real-time. Can’t try right now because I’m on a train using ARC over 4G and it’s what I’d expect. (It takes about 1-2 seconds from writing a search term to getting the result. Though there are some issues were correct terms yield no results)
Looking at logs the website (.roonlabs.com) is in California but the compute (.roonlabs.net) is hosted by Google (in the US)
I get a fairly stable 105mS response from that but looking at logs it seems to vary in the processing of requests i.e post or get requests vary between 480mS and 30000mS. I haven’t found anything faster than 480mS so far.
I’d say that any latency people are seeing is down to congestion or contention in the compute platform and not an ISP or home network/PC issue.
I get 50-70 ms ping response from roonlabs.net even from my phone on the train in Austria (data roaming with my German Vodafone mobile plan) with 4G.
Roon data requests that involve processing on the server of course would need more time
Not sure how you are getting those times as the straight line distance between Vienna and NC is 4400 miles and the fastest should be 80mS
A lot of tools use RTT smoothing but I wouldn’t expect them to drop the results that massively.
using an online tool I get the following for Vienna to Atlanta
I think that’s the main issue, if I’m seeing around 500mS for the Roon compute to process a single request that will quickly accumulate when you are running multiples to compile a page in the Roon client or search results etc.
The solution would be to put a compute cluster in Europe (preferably the UK 
) to share the load, it’s probably around a 50/50 split between NA and European users anyway. Roon already use geo location (https://geoip.roonlabs.net/geoip/1/lookup) so it would be easy to redirect the euro clients to that one instead of NA.
I think Cloudflare CDN clusters are available in Europe also. Not sure about the complete architecture of Roon though.
For what it’s worth, i have exemplary response times while pinging roonlabs.net.
With that said, now enjoy your holidays! This is not critical, and my turntables are working fine, so… 
I’m only guessing how they do it but the compute aspect of compiling search results and metadata etc will be done on their Google compute platform which then tells the client to get the data from a CDN that is closest (multiple instances anywhere in the world)
Again there’s something weird going on as it’s physically impossible for you the get 11mS round trip times from Sweden to the US.
