Caramel Coating producing inconsistent results
It is odd that the original recipe didn't include a temperature, as temperature is absolutely critical in candymaking. That is probably why your results were so inconsistent, as different pans would have heated the mixture at different rates. I would shoot for a temperature of 240-250F (Hard ball stage) as that should be thick enough to coat the nuts and allow them to finish caramelizing in the oven. 

To avoid getting the pecan brittle again, avoid excess of the coating mixture on the pan and be sure to keep the nuts moving frequently during the bake.

Here are a couple of recipes that show a similar temperature range:

Candied Orange Walnuts

Brown Sugar Walnuts