Random performance inconcistency in Unity with ARCore on Android

Hello, I'm having random issues with AR using ARCore package in Unity 2020.1.17 - note: I'm not using ARFoundation at the moment since the old ARCore system seems, unexpectedly, to have better performances also on old on low tier devices.

Here is a screenschot of profile when my AR scene comes loaded with poor tracking stability and a more than slightly delay of augmented image prefab for the tracked image. It's interesting that if I reduce application frame rate I come up having a delay for the whole camera experience but the performance issue is less likely to manifest (even if it still happens).

It leads me thinking it's not a only frame rate related issue and, since I gain a not so good lag between real world and camera experience, my goal to solve the problem is at high priority for me.

In this second screenshot, instead, the SAME SCRIPTS (no changes, same scripts at 100%) run very smoothly and no effort I tried till now could bring me to understand the causes for this weird behaviour. Another noticeable event is that when CPU show highest level (and the whole application runs with poor performances), the GPU seems to be stuck in a sort of "lazy mode". Instead, when the GPU works harder the CPU has a normal graph and performances are very good even at 50 fps!

What am I doing wrong with Unity settings? I use Update in my scripts (no Fixed or Late update), i set fps in ProjectSetting along with proper Time and Timeline options everytime. I diabled HDR, light extimation, probes, I use the mobile transparent shader (not the standard one) for my augmented content prefab

Thanks in advance for the help!