This is due to a time deviation contributed by the bug in the PCS/PPS Virtual Appliance System Clock and is not related to the NTP Server.
If this issue is hit, you will see the following log entries in the PCS/PPS Event Logs (System -> Log/Monitoring -> Admin -> Log) similar to the ones specified below,
info - Default Network::System()[][] - 2020/02/26 10:55:26 - VPN - Time adjusted by 73.81355 seconds.
info - Default Network::System()[][] - 2020/02/26 11:56:30 - VPN - Time adjusted by 73.81654 seconds.
info - Default Network::System()[][] - 2020/02/26 12:57:34 - VPN - Time adjusted by 73.80965 seconds.
info - Default Network::System()[][] - 2020/02/26 14:08:38 - VPN - Time adjusted by 73.81568 seconds.
info - Default Network::System()[][] - 2020/02/26 15:09:42 - VPN - Time adjusted by 73.82095 seconds.