Hi @nachopescado,
This is indeed an issue related to Cloudflare, as stated on the thread you referenced (Production custom admin URL displays invalid SSL - #12 by james-janetech).
You must contact the cloudflare support in order to fix this issue. We also find this concerning, but sadly there is nothing much we can do on our end for this problem.
Let us know once this is fixed, and I hope it helps 