After you submit a move, the server redirects you to your next game using a 301 response. It appears that the URL provided in this response begins with http:// instead of https:// , and this is causing Chrome to complain. Richard can fix the problem by making the URL use https.
I use Firefox, so I didn't notice the problem until the people in this thread mentioned it. If it only started happening after an LG update, my best guess is that HSTS got enabled on the server during that update. There is also a possibility that newer versions of Chrome are disallowing redirects from https to http.
Thissymptomappeared when I had a problem on my old PC and I used a new laptop to make my moves. The message appears with every move on the new laptop. I fixed my old PC this morning, and I submitted all my moves from Chrome on my old PC and the message did not appear. I thought maybe it is an issue on my Chrome on the PC, so I tried to use Chrome on my mobile, and also the message did not appear on the mobile too.
I check it on the laptop once more now, and the message appears with every submitting (even with this message posting).
I agree with Tommah regarding redirection, but this does not explain why it works fine on my PC and mobile.
I just wanted to give a better vision regarding the issue.