If a script module accesses a variable defined in a script that imports this module then this variable may or may not be found depending on call scenarios and PowerShell versions.
Test-Module.ps1 imports MyModule.psm1 and
defines $MyVariable. Then it calls the imported function Test-MyVariable
which tests $MyVariable. This variable is not found in v2.
In v5 the variable is found. At this point this may create an illusion that all
is fine. But the problem is revealed in a slightly more complex scenario. When
the working script Test-Module.ps1 is called from another
script Test-Module2.ps1 then $MyVariable is not found
again.
Scripts MyScript.ps1, Test-Script.ps1, and
Test-Script2.ps1 implement the same call scenarios using
dot-sourcing of the variable $MyVariable. All works fine.