I have an strange error in my log and I am not sure what I need to check.
Invalid value for key 'relatedByAttribute' in 'WorkoutEntity' entity. Remove this key or add attribute
This is one place what I found where I use relatedByAttribute in WorkoutEntity
Do you have an idea what can I check as well to see issue.

I had the same problem. In my case, I opened the .xcdatamodeld with an external editor, looked for the "relatedByAttribute" label and found that the label was "relatedByAttribute " instead (note the blank space). Removed the blank and worked since then. I hope it's good for you! ;)