It is a very difficult puzzle in my opinion.
Part of your solution is correct, but there is a flaw in your logic that has sent you down a dead end.
Repeating from your post:
Clue 3: Masking tape is Wednesday or Harrar. This also implies that Harrar cannot be Wednesday.
Clue 5: Masking tape is Tuesday or Sidamo. This also implies that Sidamo cannot be Tuesday.
So you are correct when you state
"So Masking tape must either be Tuesday and Harrar or Wednesday and Sidamo."
However, your next statement is incorrect:
"Sidamo not Tuesday clue 5. so must be Wed. "
Clues 3 and 5 present two possible associations for masking tape. Just because masking tape is one of those two associations, it doesn't make the other association true.
Those two associations of weekday and coffee in clues 3 and 5 are conditional on masking tape. I.e. IF
masking tape is Tuesday, then Tuesday is associated with Harrar. IF
masking tape is Wednesday, then Wednesday is associated with Sidamo.
In this case masking tape is not associated with Wednesday, so we can't say if Wednesday is associated with Sidamo or not.
The following table shows the count of new Xs (not dups) placed on successive passes through the entire list of clues as I solved the puzzle.
Pass 1 Pass 2 Pass 3 Pass 4
Clue 1 7 0 2 1
Clue 2 2 5 0 0
Clue 3 1 5 0 0
Clue 4 3 0 0 0
Clue 5 1 4 2 1
Clue 6 4 0 0 0
Clue 7 1 0 0 0
Clue 8 2 6 3 1**
** When I placed that X on pass 4, I knew where Mateo belonged, and clues 6 and 2 immediately gave me 2 more positives.
You can see on the fourth pass, the newcomer Xs were starting to get scarce, but I still got three more.
I usually don't make this many passes, but for this exercise, I didn't engage in any short cuts or combined passes. I just did a brute force (inefficient) top to bottom march through the logic. I was really curious to see how many passes it took on this difficult puzzle to finally get a positive.
I spent more than 6 hours on this one the first time I saw it. I had diagrams and flowcharts, truth tables, and guess outcomes all over the place, and lots of wadded up paper in the basket.
Keep at it.
If you can solve this one, the others are going to look easy.