sentry-python: Transaction doesn't work with FastAPI

How do you use Sentry?

Sentry Saas (sentry.io)

Version

1.38.0

Steps to Reproduce

1. Create main.py

import sentry_sdk
from fastapi import FastAPI
import time

sentry_sdk.init(
    dsn=$DSN,
    profiles_sample_rate=1.0,
    traces_sample_rate=1.0,
    environment="dev",
    release="1.0",
    debug=True,    
)

api = FastAPI()


@api.get("/sentry-debug")
async def trigger_error():
    with sentry_sdk.start_transaction(op="task", name="test2"):
        for _ in range(100):
            time.sleep(0.01)

async def test1():
    with sentry_sdk.start_transaction(op="task", name="test1"):
        for _ in range(100):
            time.sleep(0.01)

import asyncio
asyncio.run(test1())

1. run gunicorn main:api -k uvicorn.workers.UvicornWorker
2. Check sentry.io and confirm test1 showed up
3. Open http://localhost:8000/sentry-debug on browser
4. Can see this log on terminal

 [sentry] DEBUG: [Tracing] Starting <task> transaction <test2>
 [sentry] DEBUG: [Profiling] Initializing profile
 [sentry] DEBUG: [Profiling] Starting profile
 [sentry] DEBUG: [Profiling] Stopping profile
 [sentry] DEBUG: [ASGI] Set transaction name and source in event_processor: '/sentry-debug' / 'route'
 [sentry] DEBUG: [Profiling] Stopping profile
 [sentry] DEBUG: Sending envelope [envelope with 2 items (profile, transaction)]

1. Check sentry.io but don’t see test2

Expected Result

Both test1 and test2 on sentry.io

Actual Result

test1 works, but test2 doesn’t show up