Cannot get jportable 7u51 to run correctly on FFPortable 48 without full Java 7u51 installed

Hi,
I've got several Windows 10 (v1803) 64bit machines where I've tried to run jPortable in Firefox Portable without success.
We have multiple legacy systems that require Java7 and specific versions of it on browser plugin, so to be able to connect, we've used FirefoxPortable 48 and jPortable 7u51.
I also have native Java8u171 installed on the systems.
I've used this same setup in Windows 7 SP1 64bit machines for years without any problems but with Windows10 I cannot get this to work.
Java plugin does not load properly unless I have the full 'native' Java 7u51 plugin installed on the system.

When loading page (ex. https://www.java.com/verify) I get two warnings saying that 'Your Java version is out of date' and suggest to update with Block and Later options. When clicking Later, page has a white box for about 2 minutes. After that, error is displayed that says 'Were unable to verify if Java is currently installed and enabled...'
Now here's where it gets interesting; if I install native Java7u51 on the system and start the same page with FirefoxPortable, I first get the same warning saying that 'Your Java version is out of date' and suggest to update with block and Later options. After clicking the Later -option I get
Security warning saying that 'Do You want to run this application ?' and if I click Run -button, Java loads properly.

So, there's something or some setting blocking Java from loading properly when using jPortable in FirefoxPortable, unless native JRE is installed on system.

I've tried the following on Java:
-Started java control panel on .\portable\CommonFiles\Java\bin and set Security Level to Medium
-Made sure that 'Enable Java content in the browser' is enabled
-added site URL to Exception Site List

Tried the following on FirefoxPortable:
-Made sure that AlwaysUse2bit=True is set in Firefoxportable.ini

If You have any idea on what's causing this behavior, help would be greatly appreciated.