SW 2018 SP3.0
The image highlights two surfaces identical to each other with the exception of the selection on creation which causes an error.
Tangency Mate selections were faces not edges.
The resolve sometimes is to bring the items close enough together AND (MOST IMPORTANTLY) where you select on the curved surfaces prior to selecting the of tangency mate, so that SW doesn't get it confused.
This is an observation and a question as to ask if SW is going to fix this sort of erroneous type of behavior that has been going on?
What's shown is all I can show. I cannot share models.