I'm going to try a different OS this weekend. But in the meantime...
Are you able to use this camera without Mirror Lock?
Disabling Mirror Lock is just a matter or setting the Mirror Lock time to 0 on Ekos and set it to be "off" on the camera menu?
Apart from disabling "force bulb" and picking a predefined exposure time, what else do you ensure is set in order to take short exposures?