MacOS does not isolate the apps in the secondary monitor through each Desktop

I work with MacOS - El Capitan

Furthermore I have Windows 10 and Ubuntu Desktop working with multi desktops. I know how create a new one and how move through them

An important observation is that for each laptop is that each one has a secondary monitor. I am able to open any application (editor, window explorer or finder, terminal console, an IDE - etc) and move it to the secondary monitor. Therefore some applications are in the primary monitor and others in the secondary monitor.

The point here is, for each Desktop, I am able to have in the primary and secondary monitors any application. If I pass through these Desktops each Desktop respects and keeps isolated the same set of applications opened and distributed through the primary and secondary monitors from the beginning. Again it for each Desktop.

Problem: all the content (app) opened in the secondary monitor is shared through all the workspaces, therefore the apps are not isolated through each workspace.

How to fix this?

Fixed in comments.. but to provide an answer for future searchers…

Two things to check…
System Prefs > Mission Control > Displays have separate Spaces [should be off]
Then right click any one of your aberrant apps in the Dock > Options > make sure it's not set to All Desktops.

Either or both of those settings could be responsible.