Is it possible that the true serial version of the lib can’t communicate the the SoftwareSerial (SoftEasyTransfer) ?
No I’ve tested that several times with no problems.
led on the attiny flickers, stays on some time.. turns off..
That might also be issues with debouncing.
Are you still having issues? I can’t think off the top of my head what could cause this just because you are using an ATtiny.