Error - Unable to Sync. Value cannot be converted to Enum

[andreagiordano]

I'm getting this error: I have two Enum field (in different tables) where users have to choose a value. Instead of having the values listed in the  Configuration of the field 

I tried to get them from a table I can edit. In the Suggested values I put the expression "=Tablename[ColumnName] as seen in this q&a. The expression test correct and it works as I thought  but when I use it in the app I get this error when I choose a name from the list. I've seen in this q&a that I should flag "Allow other vlaues" but if I do this the field will be open to anything and I but I just want the values listed in the table. 

Another problem is that in the table I have duplicated values and I don't know how I can avoid duplicated values.