I don't post much, but I will make a few comments here involving safety and tree care (my opinion).
You don't say in your post so I'll comment that I hope you have a climbing limb attached when you are spiking up a tree. It will save you if a gaff comes out like you said it has. I have that same flipline and it is very nice. For trees with thick bark, you need to use your climbing line to assist you with the flipline. Hard to explain in type, but with climbing line and spikes holding you, make sure you have enough slack in flipline at waist level and using two hands (one on each side) pull the flipline out from the tree and fling it up. Lean back immediately so the flipline holds and spike up. You can then tighten your climbing line and flipline if needed or continue up. When the climbing line (and spikes) are holding your weight it allows you to create space with the flipline to throw it up and you need that space in rough bark trees moreso than smooth trees.
Regarding tree care, I hope you are only using spikes in trees you are removing because it does damage trees. If you are just learning to climb, take them off. You will be a much better climber if you learn without them. I climbed for 3 years trimming and removals before I bought my first pair. Yes, they are nice for when doing removals, but they are not good to learn proper tree climbing skills. Safety first, take your time, and enjoy it. The more you do it the easier it will get, but don't rely on spikes and never forget the safety aspect.