Incomplete BARs in Free tier WebSocket?

Hi there.

I’m testing the WebSocket for gathering BARs.

I subscribed to 15 stock symbols.
However, every minute I only get around ~3 BARs, instead of 15.
I’m using the Official Node.js SDK.

Anybody knows what’s the reason for that?
Is that because it’s the Free tier? Or something else?
Sorry if that’s obvious, I’m a total layman on stock-related stuff.

Thanks in advance!