Seems to be Looks like discovery database broken.
Try to access this below URL in postman and confirm you are getting the result or not?
http:/localhost:8085/client/v4/content.svc/GetPublicationMappingsFunctionImport(Url='http://localhost:8080/')
Note: Please change your registered BaseURL against your content service.
Expected result with your publication mapping id and baseURL:
<?xml version="1.0" encoding="UTF-8"?>
<entry xmlns:metadata="http://docs.oasis-open.org/odata/ns/metadata" xmlns:data="http://docs.oasis-open.org/odata/ns/data" xmlns="http://www.w3.org/2005/Atom" metadata:context="http://localhost:8085/client/v4/content.svc/$metadata#PublicationMappings/$entity" xml:base="http://localhost:8085/client/v4/content.svc">
<id>http://localhost:8085/client/v4/content.svc/PublicationMappings(NamespaceId=0,PublicationId=8)</id>
<title></title>
<summary></summary>
<updated>2018-11-28T14:11:20.775Z</updated>
<author>
<name>SDL OData v4 framework</name>
</author>
<link rel="edit" title="PublicationMapping" href="PublicationMappings(NamespaceId=0,PublicationId=8)"></link>
<category scheme="http://docs.oasis-open.org/odata/ns/scheme" term="#Tridion.ContentDelivery.PublicationMapping"></category>
<content type="application/xml">
<metadata:properties>
<data:NamespaceId metadata:type="Int32">0</data:NamespaceId>
<data:PublicationId metadata:type="Int32">8</data:PublicationId>
<data:Protocol>http</data:Protocol>
<data:Domain>localhost</data:Domain>
<data:Port>8852</data:Port>
<data:Path>/</data:Path>
<data:PathScanDepth metadata:type="Int32">100</data:PathScanDepth>
</metadata:properties>
</content>
</entry>
If there is no result, then I'm sure discovery database is broken for you.
Please raise it to SDL support.
or else, You could recreate your Discovery Service DB, register the Capabilities again and then use Sync-TtmCdEnvironment to synchronize with Topology Manager
Note:
if you add new BaseURL to existing setup not required to run the Sync-TtmCdEnvironment it will auto sync, actually where it's really required to run this command if you Exporting and importing Content Delivery information between Topology instances in a DTAP setup, then it's required to run Sync-TtmCdEnvironment
I hope it helps.