in addition to what @Ray commented, there is a possibility that the admin has disabled SSL transport as an option. this would prevent access if there is anything that drops the UDP 4500 traffic. however, based on your log snippet, there is more likely an intermediate device that is closing the heartbeat connection (TCP 443) between the client and the VPN server. can you work with your admin for a coordinated TCP dump on your client and the VPN server to make sure that the traffic is flowing properly?
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