Hi,
for me this is totally normal behavior on Linux, especially for servers with that less total memory and running some containers. There are quite a lot and good web pages around which explain exactly overcommiting means and why this happens.
there is a really good blog entry describing exactly whats happening but unfortunately it’s only in German (Linux und overcommit_memory (lug-erding.de)). I haven’t found a good practical blog after a quick search, but linux overcommit_memory would do the job.
Long story short, as Robert mentioned, higher the thresholds for this host (i would disable it completely in this case) or spend a bit more memory on this host. Additionally you can tune your system a bit to not overcommit memory but this could lead into problems with your container not starting anymore (really limited memory on this host).