I had a similar issue with my pre owned but not pre worn Riedell Silver Stars. They are older, a discontinued model, leather with no flex notch. I noticed that my ankle flexion seemed to be giving my boots a deeper crease than they should and that the ankles never really felt quite right. The actual lower boot part fit like a glove after a few weeks break in time, no blisters, snug but no significant discomfort and I could still move my toes a little. And yet the sides appeared to be breaking down, and I am a lower level skater, no jumps.
My solution was two fold. I changed my lacing technique to the Edea style, I have also heard it called the Russian Lacing technique. Basically it means that you are always taking the lace over and down into the holes instead of up through them. The reason it helped me is that it provides a more even pressure along the lace line. Looking at your boots, the one on the top that is more of a side view, appears to be laced that way already, though it is a little hard to tell, the other boot that is more a top view I cannot tell for sure because of light glare, but it looks as though it may be laced the other way (under and up through the holes). I was talking to a woman in my skate group the other day with brand new Edeas about this and we discovered her boots were laced in a combo of the Edea technique on one (done by a guy in our pro shop) and the other was incorrect at the bottom (the laces on that one came partially laced from the factory) and correct on the top (done by her). Once we figured it out it was a quick fix, but it made me realize you can actually have two patterns on the same boot, it is easy to get mixed up.
If the Edea lacing technique is correct then you will only be able to tighten the individual laces by pulling them sideways, I do it with a little jerk-jerk motion. Trying to pull them up towards you as you can with the other lacing technique feels very awkward. So, the lacing technique was one thing, the other thing I did was make my ankle slightly bigger, "stickier", and more padded by adding Bunga pads around my ankle bone and lower shin area. Often used to prevent lace bite, they are also great if you have skinny ankles.
For me, the combination of redistribution of pressure on the boot and getting my ankle to better fit in the boot stopped my boot creasing completely and made me much more comfortable. Even better, a few months after making those changes, simply adding a new pair of laces improved things even more, the laces my boots came with were too stretchy and therefore gave inconsistent pressure.