The timeline may be unavailable in dotMemory 2018.1 and earlier for one of the reasons:
• This is a remote profiling session
• The profiled app is a .NET Core, ASP.NET Core, UWP, WinRT, or Silverlight application
• The profiled app is run with administrative privileges while dotMemory is run under a user account. For example, this may be the case when you profile an IIS-hosted web app, Windows service, .NET process or attach dotMemory to a running process
• The workspace is created using the profiling API
• The workspace is created by the dotMemory Unit framework
• The workspace is created by the command-line profiler
• The workspace is created from a process dump
• The workspace is created on machine with broken or missing performance counters.
Follow this article to detect and solve performance counters issue.