A too thick emulsion layer makes bubbles when drying.
2. Possible origins
You didn't remove the black rubber parts of your scoop coater, which are only there to protect it during transport.
You need to practice the coating movement a little more.
3. Solution
If you didn't expose your screen yet, you can just clean it with water and a sponge. If you already hardened the emulsion, you need to reclaim your screen before using it again.
