The MyWatch face is my favorite, but as has been noted by many others, it crashes periodically and must be uninstalled then reinstalled to get it working again until the next crash. The developer has not issued any updates recently and may have moved on, however I've been doing some experimenting. I am most definitely not a developer, but I noticed that if I install the WF and DO NOT use the GPS method to get the sun data working, but rather leave it uncalibrated, the watch face crashes much less frequently. I've had multiple days with out crash as long as I don't display the sun data.
I'm not sure what's behind this, but it makes this WF a bit more usable and may help other developers continue trying to resolve the crash issue with their watch faces.