We're aware of an issue in myIR where an L letter will not send if a client has D status for an earlier tax year. The message displays “This client has a current D (Deferred) status request".
Until a fix is in place you can still use the Tax agents self-service line, 0800 456 678, to request up to 10 L letters at a time. You'll need your PIN number - call us if you need it reset.
We'll provide an update here when we have a fix in place.