2019.3.0b8 freezing in AssetImportManager::Import

Crossposting from beta forum

Some devs of our team already using the beta is experiencing frequent freezes.
The lock up can happen during startup, or on any asset change or during build.

I attached VS2019 to Unity.exe, and I see the main thread is stuck in

AssetImportManager::Import

Here's the call stack of the main thread:

Code (CSharp):

1. >    ntdll.dll!NtWaitForSingleObject()    Unknown
2.      KernelBase.dll!WaitForSingleObjectEx()    Unknown
3.      Unity.exe!AssetImportManager::Import(class core::hash_map<struct AssetDatabase::ImporterID,struct ImporterInfo,struct core::hash<struct AssetDatabase::ImporterID>,struct std::equal_to<struct AssetDatabase::ImporterID> > const &,struct dynamic_array<struct PostprocessorInfo,0> const &,class AssetResolver &,struct CategorizedAssets &,class IImportProgress *,class core::hash_set<struct UnityGUID,struct core::hash<struct UnityGUID>,struct std::equal_to<struct UnityGUID> > const &,struct LoadedImportedAssetsSnapshot const *,class core::hash_set<class core::basic_string<char,class core::StringStorageDefault<char> >,struct core::hash<class core::basic_string<char,class core::StringStorageDefault<char> > >,struct std::equal_to<class core::basic_string<char,class core::StringStorageDefault<char> > > > &,class CrashedAssetImportsDatabase &,class core::hash_set<struct ArtifactKey,struct core::hash<struct ArtifactKey>,struct std::equal_to<struct ArtifactKey> > &)    Unknown
4.      Unity.exe!ImportAndPostprocessOutOfDateAssets()    Unknown
5.      Unity.exe!RefreshInternalV2()    Unknown
6.      Unity.exe!StopAssetImportingV2()    Unknown
7.      Unity.exe!RefreshV2(enum AssetDatabase::UpdateAssetOptions)    Unknown
8.      Unity.exe!AssetDatabase::Refresh(enum AssetDatabase::UpdateAssetOptions)    Unknown
9.      Unity.exe!Application::InitializeProject(void)    Unknown
10.      Unity.exe!WinMain()    Unknown
11.      Unity.exe!__scrt_common_main_seh()    Unknown
12.      kernel32.dll!00007ff9a1847bd4()    Unknown
13.      ntdll.dll!RtlUserThreadStart()    Unknown
14.  

Disassembly shows:

Code (CSharp):

1. 00007FF7E16F7DF4  call        RemoteAssetCache::GetArtifactFromCacheServerAsync (07FF7E16F5E80h)
2. 00007FF7E16F7DF9  nop         dword ptr [rax]
3. 00007FF7E16F7E00  mov         edx,0FFFFFFFFh
4. 00007FF7E16F7E05  mov         r8d,1
5. 00007FF7E16F7E0B  mov         rcx,qword ptr [rbp+50h]
6. 00007FF7E16F7E0F  call        qword ptr [__imp_WaitForSingleObjectEx (07FF7E4BF9C10h)]
7. 00007FF7E16F7E15  test        eax,eax  

I guess it waits for that async fetch to complete...
Editor.log doesn't contain anything useful.