Why is my sub domain SSL not working on Shopify anymore?

[SallyDells]

We set up a sub domain in our Shopify account to redirect customers scanning QR codes in our recipe book to videos that are hosted on our Shopify account. 

We set up the sub domain as instructed by the QR code generator. All was working fine for at least one month, we were able to scan all the QR codes and get taken to the correct videos on our Shopify site as planned. 

However last weekend they all started to fail to scan, and when scanned we are given a "non secure server" error message. 

I contacted Shopify who tried to re issue the SSL but this failed. I was then told to change where the CNAME points to in the DNS. This did not help as the CNAME has to point to "cname.q-r.to" in order to work. (instructions for QR code generator). 

I finally got in contact with the support at QR code generator and they have told me that the only way to issue an SSL is through them after upgrading to their top tier account. And even after being issued this SSL this will change the QR codes!!

We absolutely cannot change/re-issue the QR codes as this will void the current ones and make them un scannable. We CANNOT DO THIS because they are already printed in our recipe book!!! 

What nobody has been able to answer is why this was working and now its not!! If it was working surely there is a way to get it working again with out messing up the printed QR codes.

I really need some help with this if there is anyone out there that can please please contact me! 

Thank you! Sally