Thank you for replying!
Well, so far, I made approximately 25-30 levels and I only had this problem recently with 2 levels, but I'm afraid there will be more. I doesn't seem to be happening with specific level types (cave, castle etc..).
I'm not editing the overworld at all, only the levels.
These levels, where the game will show everything except for the Yoshi coins are:
-Donut plains 2 (underground) [9]
-Donut plains 3 [5]
In the help file I only found one place corresponding to the coins or Y. coins and that is "Change properties in header".
Now there, it says that the memory index setting should be 0 on the main level and 1,2,3,4 on the sub levels. That is how it is, so it should be in working order.
I'm really annoyed by this, because one of the rewards for the player in Mario games, for exploring the levels are Yoshi coins.
So now, when the player takes the time to actually wonder in these not so obvious directions, finds nothing instead of a Yoshi coin..
Thanks again for taking the time to reply!
Looks like Bowser's at it again!