I have the same problem: it seems that QHY6 driver works well when you try to guide for the first time (I guide a Skywatcher EQ8 through EQMod), but if you stop guiding and later you try to restart guiding, the driver fails. Even the QHY6 dissapears from the camera menu and only remains the science CCD (in my case, the SBIG ST-8 XME). It seems this problem is quite common, I know another friend with the same problem.
I'm going to replace the QHY6 by an ASI 120MM, hope this CMOS won't give these problems.
Apart from this but, Ekos seems great: I'm currently migrating from SGPro to Ekos and it is much more lighter than the heavy and slow SGPro. The plate solve and the overall program are very fast compared with SGPro and guiding is fine when the QHY6 works.