When flushing toilet, water level is fine. Within minutes it drops 1/2 inch
And the tub gurgles.

What could be the problem.

I had the sewer line snaked.

Put water in roof vent and did not see blockage. I snaked the toilet.

I put liquid plumber in the tub.

After 4 or 5 flushes, sound went away. But it always returns.

Is it okay to live with this?

Although you had the drain snaked and poured water down the vent you still have an issue. You have to put a great deal of water down a vent before you can tell if there is a problem. Put a garden hose in the vent and let it run for 10 minutes. Septic or city sewer?

There is no doubt that you have a blockage in the lavatory roof vent.
The solution would be to snake the roof vent. Put out on enough snake to reach the base and 15 more feet. Good luck, Tom