Macs fail to reach IBCM Proxy, pma_agent.log contains errors:
04-05 10:54:04.311 D RpcLocator /CmProxyCommUtils:73:307/ Calling CM Proxy at https://your.domain.com/ParallelsMacManagement/.rpc
04-05 10:54:04.313 D /RpcClientCpp:73:1d03/ Connecting to 'your.domain.com' (126.96.36.199)...
04-05 10:54:04.730 D /RpcClientCpp:73:1b0b/ Successfully connected to '188.8.131.52'
04-05 10:54:05.241 W RpcLocator /CmProxyCommUtils:73:1b0b/ Call failed with 54 (Connection reset by peer)
04-05 10:54:05.242 I CmProxyLocator /CmProxyCommUtils:73:1b0b/ Failed to locate CM proxy.
04-05 10:54:05.242 W /PolicyAgent:73:1b0b/ PolicyAgent: connect failed with 54 (Connection reset by peer)
04-05 10:54:05.244 D /LocalIpc:73:307/ LocalIpcConnectionImpl::onError() : 1 (QLocalSocket: Remote closed)
IBCM is resetting the connection as valid PKI certificate is missing on Mac.
In most cases it is because PMM is configured in non-PKI mode.
Configure PMM in PKI mode.