Insulated Fastrack

#1 ensure the cut rail portions on either side is properly connected to the crossing and line up to the sensing rail side.

Underneath the crossing tells you which outside rail side is the sensing rail and MUST be isolated with the external cut rail tracks and no track in between can have the shorting bus bar.

#2 any pieces of track in between the cut and the crossing need the shorting bus bar removed. Your cut 5 inch pieces are KNOWN to also have the bus bar and if that end is placed towards the crossing you defeat the insulated rail and cut section.

Seen around the 7:50 mark or so in the linked video

Key point, this is the same as an insulated rail. It actually has to be isolated so it can sense the wheels shorting it to the other rail.

https://www.youtube.com/watch?v=DRE-W-0hUr4

Also this video specific to the grade crossing. https://www.youtube.com/watch?v=c38daqUm8i4

Again, possibly part of the fail is this:

"they sent 2 pcs of 5" regular Fastrack. This obviously will not work. I took my Dremel tool and cut one of the outside rails on each pc to see if that would work."

Again, known fact, 5 inch pieces that were normal non-cut insulating pieces ALSO from the factory had a shorting bus bar.

Between not removing that bus bar, and or it being on the wrong side of the cut or break, and or not aligning the cut rail on both sides of the crossing with the sensing rail marks, you effectively short the sensing rail to outside rail of the rest of the track and thus no longer a sensing rail. It senses there is a train all the time.