Hi!

When Trix C track is made, the rails are electrically connected. Usually this connection is cut at the factory. But sometimes they forget about it.

If that is the issue, then you can simply cut a small bridge that electrically connects both rails. This bridge should have been cut with all your working C track pieces.

Here is a piece of Märklin C track where I cut that bridge (red circle).

You have to check those small bridges at both ends.