I'm not really familiar with the notions of short chain and long chain 
. So there is no reason why I'm using the short chain, and I think I didn't try to use the long one.
What do I have to do to use the long chain please ? 
(I read the following article Providing a longer certificate chain by default to understand what a long chain is, but do I have it and am using the wrong file, and did I do something wrong when renewing ?)