Alexa/Echo - Invoking a Skill with Intent via Echo vs. Testing with text

I have an Intent that is a sentence like:

Tell us about {Topic}

A topic could be a few things from a list (custom slot type), each item can be between 1 and 3 words.

When I open the skill first ("Alexa, open Skill Name"), and then test it with all topics on Echo (voice) or via the service simulator (text), it works.
When I invoke the skill with an intent ("Alexa, ask Skill Name to tell us about Topic"), and test it with all topics using the text service simulator on the portal - it works.
But when I invoke the skill with an intent, and test it with Echo (voice) - only some of the topics work and the other fail to be recognized.

Any hint will be greatly appreciated. Thank you.

Solution

So the Echo is mis-interpreting some of the topics - that is not uncommon. I find that when I actually started testing, the voice recognition was not as good as I thought it was going to be.

Why the recognition would be better when you open the skill first is a mystery since that part of the process is a black box - it could be something subtle to do with voice recognition, eg. the spoken sentence is different and more complicated in the fail on echo case (#3 above) vs. the succees on echo case (#1).

When you say "fail to be recognized" - do you mean that it returns an incorrect word?