the tpu based filaments do tend to print best at fairly low temps. I suspect running it at 250 could be your problem.
At that temperature it'll be so liquid that you might not be getting it all through the nozzle, and as residue builds up it'll interfere with the print.
Just a thought.

The trick with flexible filaments is finding the optimum temperature for your printer that give a clean print and also allows the filament to be pushable through the nozzle.
I've gone off the tpu based filaments at the moment and use polyflex flexible pla. It prints best at 220 - on my machine - makes very clean prints and is a little stiffer than the tpu. It's at least as tough and flexible. But has way fewer printing issues.

eagleseven your ctc should print as high as 260 without any issues.