The admin UI and the product UI both use the Apache2 service (think it is still the same in the later versions) but two separate instances/services that is why you can have one running and the other not.
You can check the state of the services. Iam not sure of the CLI someone else may post it here but i use the REST api
https://insert you vrops node/suite-api/api/deployment/node/services/info
you will get this. It will show you if the service for the adminUI is stopped. You could command line it to try and start it but i would have to google the command.
"service": [
{
"name": "LOCATOR",
"health": "OK",
"details": "Success, Service LOCATOR is running and responding",
"uptime": 605626174,
"startedOn": 1586945859917
},
{
"name": "ANALYTICS",
"health": "OK",
"details": "Success, Service ANALYTICS is running and responding",
"uptime": 605616425,
"startedOn": 1586945873083
},
{
"name": "API",
"health": "OK",
"details": "Success, Service API is running and responding",
"uptime": 605612851,
"startedOn": 1586945873337
},
{
"name": "ADMINUI",
"health": "OK",
"details": "Success, Service ADMINUI is running and responding",
"uptime": 605632817,
"startedOn": 1586945853468
},
{
"name": "EPOPS",
"health": "OK",
"details": "Success, Service EPOPS is running and responding",
"uptime": 605612968,
"startedOn": 1586945873337
},
{
"name": "UI",
"health": "OK",
"details": "Success, Service UI is running and responding",
"uptime": 605632845,
"startedOn": 1586945853468
},
{
"name": "COLLECTOR",
"health": "OK",
"details": "Success, Service COLLECTOR is running and responding",
"uptime": 605614780,
"startedOn": 1586945871585
},
{
"name": "CASA",
"health": "OK",
"details": "Success, Service CASA is running and responding",
"uptime": 605846377,
"startedOn": 1586945640197
},
{
"name": "CASSANDRA",
"health": "OK",
"details": "Success, Service CASSANDRA is running and responding",
"uptime": 605672816,
"startedOn": 1586945813605
