Multicall taking 300 seconds to return result - python-3.x

Question

I am using python multicall library (https://github.com/banteg/multicall.py) to get the ERC20 balances with multiple wallet addresses at once with multiprocessing.
Once the process starts multicall returns the result in less than 1 sec, but once this process continues & run for hours it starts giving results in more than 1 min sometime it takes up to 300 secs too.
Can anyone answer the reason behind the latency in response by time.
Below is the code sample:
block_number = 11374651
GET_BALANCE_FN = "balanceOf(address)(uint256)"
def call_back_obj(success, value):
"""
Callback to process results from multicall for a function.
If call fails returns False (if changed to string throws error)
"""
if success is True and type(value) == bytes:
return value.decode("utf-8")
elif success is True:
return value
else:
return False
def get_instance():
web3_instance = Web3(
Web3.HTTPProvider(
node_provider,
request_kwargs={"timeout": 10},
)
)
web3_instance.middleware_onion.inject(geth_poa_middleware, layer=0)
return web3_instance
w3 = get_instance()
def token_balance_handler(addresses, block_number=None):
calls = []
for address_map in addresses:
contract_addr = address_map.get("tokenAddress")
wallet_addr = address_map.get("walletAddress")
calls.append(
Call(
contract_addr,
[GET_BALANCE_FN, (wallet_addr)],
[[f"{wallet_addr}-{contract_addr}", call_back_obj]],
)
)
return Multicall(
calls, _w3=w3, block_id=block_number, require_success=False
)
print(token_balance_handler(addresses, block_number)())