Xcode 10.2.1 xcode simulators are not working

after updating to xcode 10.2.1 simulators are not working.My using mscOS Mojave Version 10.14.4 in my Mac mini (Late 2012). The Simulators takes 20-30mins to attach the apps and after waiting for that much it gives error messages like "could not attach to pid:980","could not attach to pid:1020", "DTServiceHubClient failed to bless service hub for simulator". After this error message system starts lagging, performance slows down drastically.

I tried everything, Cleaning build folder, resetting simulator, reinstall xcode, updated mac OS, checked the host.txt file it includes localhost line, ping is also right. Please help me I have no idea what to do.

I was having the same issue after upgrading to macOS 10.15.3 Catalina with Xcode 11.3.1.

TL;DR

I had to reinstall macOS over the installation using recovery - but please try all the other steps prior to that though, and here's why:

My update procedure was rather unusual:

• installing 10.15 externally to a fast SSD
• building up the installation with all cloud storages and software that I needed gradually when I had the time
• keep on working with my proven 10.14 installation during day to day work
• once I had a certain installation level on the new installation, cloning the internal 10.14 installation to another external drive with Carbon Copy Cloner (CCC) (and confirming that it did boot and work)
• erasing the internal storage and cloning from the new installation of the external drive to the internal storage

Phew – I know, that's involving a lot, but that's just the way I did it... And I like to do this every once in a while just to get rid of software I once installed for reasons but that I am not using any more (and probably forgot about...).

Anyway, when cloning to the internal flash, CCC through a warning at me, that a file had not been cloned as it should have:

So I thought that maybe missing this com.apple.TCC file wouldn't be a big deal cause it might get rebuilt upon boot or whatever – so I gave it a try anyways and booted from the internal storage.

Everything seemed to be working as expected – expect not being able to run any of my projects in a Simulator from Xcode. So I researched and tried a view things that did not work.

When I was at the point where I almost broke in and considered reinstalling internally from scratch again (Ofer having deleted and reinstalled Xcode I have to add), I thought, maybe I could try and just install macOS over it through Recovery.

All that is to say that: after having installed macOS over the cloned installation, my projects attach just fine to the Simulator again.

I am not quite sure whether com.apple.TCC really had anything to do with it, but I can at least say that reinstalling save my bacon...

(Perhaps installing the latest Xcode Beta 11.4 or waiting for that to get out of Beta would have helped also, but neither of those two where an option for me at this stage)

Hope this might help anyone running into this issue...