[SalesForce] Receiving Error: Entity of type ‘flow’ named ‘xxxxxxxxxxxx’ cannot be found when doing an sfdx force:source:pull command

I'll answer as I did find some kind of workaround

Those steps allow me to work DX-style with Managed Package, Namespace and Person Account

1 Create scratch org WITHOUT Namespace, using flag -n, --nonamespace

sfdx force:org:create -f config/project-scratch-def.json -a ScratchNONameSpace -s -n

2 First thing is to pull Account.Business_Account, which works as expected

$ sfdx force:source:status -r

=== Source Status
STATE       FULL NAME                 TYPE        PROJECT PATH
Remote Add  Account.Business_Account  RecordType

$ sfdx force:source:pull

=== Pulled SourceSTATE  FULL NAME                 TYPE        PROJECT PATH
Add    Account.Business_Account  RecordType  force-app/main/default/objects/Account/recordTypes/Business_Account.recordType-meta.xml

3 Create scratch org WITH Namespace

sfdx force:org:create -f config/project-scratch-def.json -a ScratchWithNameSpace -s

4 Check status, you'll see conflicts

$ sfdx force:source:status
=== Source Status
STATE                      FULL NAME                 TYPE        PROJECT PATH

Local Add (Conflict)       Account.Business_Account  RecordType  force-app/main/default/objects/Account/recordTypes/Business_Account.recordType-meta.xml
Remote Changed (Conflict)  Account.Business_Account  RecordType  force-app/main/default/objects/Account/recordTypes/Business_Account.recordType-meta.xml

5 Push your code using flag -f, --forceoverwrite

$ sfdx force:source:push -f
=== Pushed Source
STATE  FULL NAME                 TYPE        PROJECT PATH

Add    Account.Business_Account  RecordType  force-app/main/default/objects/Account/recordTypes/Business_Account.recordType-meta.xml

$ sfdx force:source:status
=== Source Status
No results found

After that you would be able to push/pull without issues.

Make sure that "resolveRefs" and "saveRefs" are set to true. For you basically it should be enough to set "saveRefs" to true for litify_pm__ChildObj2__c. When sfdx cli inserts its (litify_pm__ChildObj2__) records the "saveRefs" flag tells if Ids should be cached (remembered) for use by other objects.

It is very well explained by sfdcfox at What Are saveRefs and resolveRefs?

{
        "sobject": "Account",
        "saveRefs": true,
        "resolveRefs": true,
        "files": [
            "Accounts.json"
        ]
    }
    {
        "sobject": "litify_pm__ChildObj2__c",
        "saveRefs": true,
        "resolveRefs": true,
        "files": [
            "litify_pm__ChildObj2__cs.json"
        ]
    }