On windows machine I'm got the below error for relay-modern

[softglance]

Relay Watcher was exited!
{ Error: spawn yarn ENOENT
at _errnoException (util.js:1024:11)
at Process.ChildProcess._handle.onexit (internal/child_process.js:190:19)
at onErrorNT (internal/child_process.js:372:16)
at _combinedTickCallback (internal/process/next_tick.js:138:11)
at process._tickDomainCallback (internal/process/next_tick.js:218:9)
code: 'ENOENT',
errno: 'ENOENT',
syscall: 'spawn yarn',
path: 'yarn',
spawnargs: [ 'relay', '--', '--watch' ] }
Relay Watcher was exited!

[nodkz]

Try to change https://github.com/nodkz/relay-northwind-app/blob/master/tools/startDevServers.js#L104

- const childProcess = spawn('yarn', ['relay', '--', '--watch'], {
+ const childProcess = spawn('npm', ['run', 'relay', '--', '--watch'], {

If it will work on your machine, please open PR with this fix.
Tnx.

[nodkz]

Try to pull last changes from master and run them