Google Calendar and Meeting don't work in Proxy way

We are using the PAC file to help our colleagues access some websites when they are in China. However, we find that Google Calendar and Meeting are not working in this way. As we test, the traffic to the below three FQDN doesn't go through our Proxy server but other traffic is all working fine:

calendarsync-pa.googleapis.com

stun.l.google.com

meetings.googleapis.com

Please let me know if is there any way to solve this. Thank you.