I am guessing this is the problem in this case and found similar error in this Converting Ubuntu 16.04 LTS
2018-12-26T10:25:18.288-05:00 info vmware-converter-worker[03052] [Originator@6876 sub=Default] Impersonating user Administrator in session 52b088da-76df-3fec-43eb-ab14faedd124
2018-12-26T10:25:31.064-05:00 info vmware-converter-worker[03052] [Originator@6876 sub=Default] Could not find the session object cache, will create a new one
2018-12-26T10:25:31.064-05:00 info vmware-converter-worker[03052] [Originator@6876 sub=Default] Obtaining query results for host 172.26.144.124
2018-12-26T10:25:42.353-05:00 warning vmware-converter-worker[03052] [Originator@6876 sub=Default] Converter::Util::SysCommandWrapper::LogResult: Command return code: 249
2018-12-26T10:25:42.353-05:00 warning vmware-converter-worker[03052] [Originator@6876 sub=Default] Converter::Util::SysCommandWrapper::LogResult: Command stderr:
--> 28:eb:bc:24:bd:67:2f:95:62:f2:d6:6f:97:b2:f1:ec
-->
2018-12-26T10:25:42.353-05:00 error vmware-converter-worker[03052] [Originator@6876 sub=Default] [Converter Agent SysinfoQuery] while trying to execute "C:\Program Files (x86)\VMware\VMware vCenter Converter Standalone\plink.exe -noprompt -stdin-pass-and-key <ConverterPrivateKeyEnd> -P 22 -thumbprint <emptyThumbprint> root@172.26.144.124 file -L /sbin/init" received error code (249) with result: 28:eb:bc:24:bd:67:2f:95:62:f2:d6:6f:97:b2:f1:ec
-->
2018-12-26T10:25:42.353-05:00 error vmware-converter-worker[03052] [Originator@6876 sub=Default] [Converter Agent SysinfoQuery] ssh connection to host 172.26.144.124 failed because the host thumbprint was different: client: <emptyThumbprint>, host: 28:eb:bc:24:bd:67:2f:95:62:f2:d6:6f:97:b2:f1:ec
2018-12-26T10:25:42.353-05:00 error vmware-converter-worker[03052] [Originator@6876 sub=Default] Sysinfo Query failed with error [Converter Agent SysinfoQuery] ssh connection to host 172.26.144.124 failed because the host thumbprint was different: client: <emptyThumbprint>, host: 28:eb:bc:24:bd:67:2f:95:62:f2:d6:6f:97:b2:f1:ec
2018-12-26T10:25:42.354-05:00 info vmware-converter-worker[03052] [Originator@6876 sub=Default] Scheduled timer canceled, StopKeepAlive succeeds
2018-12-26T10:26:08.281-05:00 error vmware-converter-worker[03704] [Originator@6876 sub=Ufa.HTTPService] Failed to read request; stream: <io_obj p:0x01d53404, h:-1, <pipe '\\.\pipe\vmware-converter-worker-soap'>, <pipe '\\.\pipe\vmware-converter-worker-soap'>>, error: class Vmacore::TimeoutException(Operation timed out)
2018-12-26T10:28:38.457-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] Obtaining query results for host 172.26.144.124
2018-12-26T10:28:57.431-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] Converter::Util::SysCommandWrapper::LogCommand: Command 'C:\Program Files (x86)\VMware\VMware vCenter Converter Standalone\plink.exe' with the following arguments:
2018-12-26T10:28:57.431-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] args[0]: -noprompt
2018-12-26T10:28:57.431-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] args[1]: -stdin-pass-and-key
2018-12-26T10:28:57.431-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] args[2]: <ConverterPrivateKeyEnd>
2018-12-26T10:28:57.431-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] args[3]: -P
2018-12-26T10:28:57.431-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] args[4]: 22
2018-12-26T10:28:57.431-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] args[5]: -thumbprint
2018-12-26T10:28:57.431-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] args[6]: 28:eb:bc:24:bd:67:2f:95:62:f2:d6:6f:97:b2:f1:ec
2018-12-26T10:28:57.431-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] args[7]: root@172.26.144.124
2018-12-26T10:28:57.431-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] args[8]: cd /tmp/.vmware-sysinfo-uwhytdyozxyrtpyr/; ./vmware-sysinfo.sh
2018-12-26T10:28:57.431-05:00 info vmware-converter-worker[03440] [Originator@6876 sub=Default] args[9]: --noLogOutput
2018-12-26T10:30:31.048-05:00 info vmware-converter-worker[02980] [Originator@6876 sub=ThreadPool] Thread enlisted
2018-12-26T10:38:57.638-05:00 error vmware-converter-worker[03440] [Originator@6876 sub=Default] Converter::Util::SysCommandWrapper::Invoke: C:\Program Files (x86)\VMware\VMware vCenter Converter Standalone\plink.exe did not finish producing output after 600 seconds