Your should be able to click on the ! icon and find out some details. In Google Chrome, click on the small shield you’ll see on the right side of the address bar, there is a script that is not loading over https, that is the mixed content issue @sandro pointed out. I do not see the invalid CA you posted about orginally.
After some testing, I can confirm that I have a problem with SSL when I access my website over home wifi but when I connect over the mobile internet it works fine.
Over WiFi
fl=120f1 h=www.mrdjaphoto.com
ip=178.148.94.240
ts=1542410321.166
visit_scheme=https
uag=Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.102 Safari/537.36
colo=BEG
spdy=h2
http=h2
loc=RS
tls=TLSv1.3
sni=plaintext
Over Mobile
fl=120f4 h=www.mrdjaphoto.com
ip=212.200.65.92
ts=1542410409.119
visit_scheme=https
uag=Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.102 Safari/537.36
colo=BEG
spdy=h2
http=h2
loc=RS
tls=TLSv1.3
sni=plaintext
Thats once again different from the screenshot you posted
Anyhow, you are using the same PoP for both connections, so it shouldnt be a certificate issue. Considering it listed the same user agent I’d also assume you tested it from the same device, hence we should be able to rule that out as well.
One other explanation I might have is that the connection is actually “hijacked” over your WiFi connection, but for that we’d need to have a screenshot of the certificate it presents to you. Opening a support ticket might possibly be the best course of action.
At this point I’d really look into which certificate it tries to hand you. That might very well be a local issue with your Wifi connection. Can you check that?
Did you install a Cloudflare Origin certificate on your server? That seems to be what you get when you request it on the Wifi connection.
However that contradicts the trace output earlier and thinking of it, you should have got that error for that URL as well. I am afraid something doesnt add up here.