timeout not work in asyncClient

[lyg4795]

I create a asyncClient by 'async with httpx.AsyncClient(proxies=proxies,timeout=2.0)as client:'
then I send a request
print("get cookie res start", f'xid{xid}')
cookieres = await client.get(url, headers=headers)
print("get cookie res ",f'xid{xid}',t-time.time())
sometimes the requests will cost more than 2s
get cookie res xid0 -4.54197096824646
and sometimes I have to wait several minutes and get an error like httpx.readError