Two Changes at the Same Time

I usually don't talk about technology here (which makes me I wonder why...) but here I go:

Bought a new phone -

Different, in its own way.

Installed an alternative OS -

Fancy, in its own way.

A different phone. A fancy OS.

In my area, it's well known that if you implement two changes at the same time, you probably will not be able to easily separate the effects from each of them - therefore this practice is not listed among the best ones.

So it is: new phone, new operational system, and suddenly there was a situation where one could not say which was not working properly...

Where are the flaws? In the different phone? In the fancy OS? On both combined? Most likely, but I cannot see...

Will I need "goggles" to see it through?