WP Switching pages vs refresh

plugin works OK on home page, not when switching to other pages.
If I (hard?) refresh page then plogin code is executed.

It has to do with how wp handles loading of scripts(?) when you switch to another page.
I read about this years ago but I CANNOT FIND the docs now.
It is NOT an apache cache problem, I am pretty sure about that, more how wp works.

Pls help me find docs, all searches I’ve tried point to ‘how to reset cache’ and similar issues.

plugin: wpcloudy
wp: 4.9.2
server: local