It's one of the most common and demoralising plateaus: you follow along fine, then go blank when you have to produce.
Comprehension and production are different skills
Recognising words as they arrive (a passive skill) is far easier than retrieving and assembling them in real time (an active one). One racing ahead of the other is expected, not a sign something is wrong.
Why input alone won't fix it
More listening and reading grows your comprehension — not your speaking. Speaking is its own skill, and it improves mainly by speaking.
The role of fear
The freeze is often anxiety about making mistakes rather than missing knowledge. Lower the stakes — accept that errors are part of it — and the words you already have tend to come loose.
How to close the gap
Practise frequent, low-pressure output; keep a stock of memorised chunks and phrases you can deploy instantly; and work on thinking in Spanish rather than translating from your first language. Even short daily speaking reps move you faster than more silent input.