If you drop into debugger, don't hit 'abort restart, invoke either 'rerun-flow-block or 'skip-flow-block after fixing a problem. If that doesn't help and you keep getting an error - still don't 'abort, but run (gamekit:stop) in the REPL and then invoke 'skip-flow-block restart - that should shutdown the engine gracefully, and you should be able to #'gamekit:start your game again. If all goes left, then just restart the implementation (should be a very rare thing). That's not very convenient and gonna be fixed in https://github.com/borodust/trivial-gamekit/issues/40.