Are you using the 1/4 inch x 1/4 inch square notch trowel for the right tile?
This is the most common size notch trowel for tile but it should only be used on the correct things. Is this right notch trowel for subway tile? What about large subway tile? Glass tile, mosaics, cement board?
See this trowel on Amazon
1/4 x 1/4 square notch trowel: amzn.to/3rU2LnM
As an Amazon Associate, I earn from qualifying purchases.