Wireless Drawbar Replacement Questions

Did you check the connector inside the locomotive?  I've had several of those loose, and that causes a problem even though the drawbar to the tender is properly secured.

To connect the drawbar, I lay the locomotive and tender on a towel next to the track and connect them where I can see them and manipulate them easily.  Then I carefully roll it up on the track as a unit.  I do the diesel tethers the same way.

It's not hard to replace the drawbar, they come in various lengths to allow closer coupling for wide curves.

You can feel the "click" when the drawbar is fully seated; don't trust a "look". I bought a set of three sizes of drawbars for $30 in the thought of "tightening-up" the gap between the engine and tender. Just stepping down one size caused problems on even 081 curves. So I went back to the original.

Replacement is as simple as one screw. There's a little spring and a couple of washers. Just pay attention and put it back together like it came apart. On a 1-10 scale, I'd rate this job as a 1.5.

This can be a damaged draw bar, where the pin solder joint is cold/cracked.  This can be as John said a loose connector in the engine.

I have also seen defective connectors in the engine and tender.  In one case as you piushed the draw bar into the tender it pushed the connector out of the holder in the tender.

Sounds like you are loosing the serial data line.  The best way to get at this is remove the engine and tender shell, connect the engine and tender together and trace the path for continuity with a Voltmeter.

I believe the replacement draw bar is $10 or 12.   G

And make absolutely sure the plastic insulator is securely in place between the draw bar and the trailing truck.